* src/tgba/tgbagraph.hh (new_state, new_states, new_transitions, out,
trans_data): Delegate these useful graph methods so we do not have to
call get_graph().
* src/graphtest/tgbagraph.cc, src/tgbaalgos/dtbasat.cc,
src/tgbaalgos/dtgbasat.cc, src/tgbaalgos/dupexp.cc,
src/tgbaalgos/emptiness.cc, src/tgbaalgos/lbtt.cc,
src/tgbaalgos/powerset.cc, src/tgbaalgos/randomgraph.cc,
src/tgbaalgos/sccfilter.cc,
src/tgbaalgos/sccinfo.cc,src/tgbaalgos/simulation.cc: Simplify.

These were only used by the BDD-based implementation of TGBA, which has
been removed.

* src/tgba/bdddict.cc, src/tgba/bdddict.hh, src/tgba/bddprint.cc: Remove
support for now/next variables.

This translator algorithm is seldom used in practice because we work
with explicit automata everywhere, and this is only useful to build
symbolic automata.  Furthermore, the symbolic automata produced by this
algorithm are larger (when looked at explicitly) than those produced by
ltl2tgba_fm or other explicit translators.

The nice side effect of this removal is that we can also remove a lot of
supporting classes, that were relying a lot on BDDs.

* src/tgba/public.hh, src/tgba/statebdd.cc, src/tgba/statebdd.hh,
src/tgba/succiterconcrete.cc, src/tgba/succiterconcrete.hh,
src/tgba/tgbabddconcrete.cc, src/tgba/tgbabddconcrete.hh,
src/tgba/tgbabddconcretefactory.cc, src/tgba/tgbabddconcretefactory.hh,
src/tgba/tgbabddconcreteproduct.cc, src/tgba/tgbabddconcreteproduct.hh,
src/tgba/tgbabddcoredata.cc, src/tgba/tgbabddcoredata.hh,
src/tgba/tgbabddfactory.hh, src/tgbaalgos/ltl2tgba_lacim.cc,
src/tgbaalgos/ltl2tgba_lacim.hh, src/tgbatest/bddprod.test,
src/tgbatest/mixprod.cc, src/tgbatest/mixprod.test: Delete all these
files.
* bench/ltlcounter/Makefile.am, bench/ltlcounter/README,
bench/ltlcounter/plot.gnu, bench/ltlcounter/run, src/tgba/Makefile.am,
src/tgbaalgos/Makefile.am, src/tgbatest/Makefile.am,
src/tgbatest/cycles.test, src/tgbatest/dupexp.test,
src/tgbatest/emptchk.test, src/tgbatest/ltl2tgba.cc,
src/tgbatest/ltl2tgba.test, src/tgbatest/ltlcross.test,
src/tgbatest/ltlprod.cc, src/tgbatest/spotlbtt.test,
src/tgbatest/wdba.test, src/tgbatest/wdba2.test,
src/tgba/tgbaexplicit.hh, wrap/python/ajax/ltl2tgba.html,
wrap/python/ajax/spot.in, wrap/python/spot.i,
wrap/python/tests/interdep.py, wrap/python/tests/ltl2tgba.py,
wrap/python/tests/ltl2tgba.test: Adjust.

* src/tgbaalgos/powerset.cc, src/tgbaalgos/powerset.hh:
Use tgba_digraph.
* src/tgba/tgbagraph.hh: Improve interface.
* src/tgbaalgos/minimize.cc, src/tgbatest/powerset.cc: Adjust.

This was only used in ELTL stuff, which I just removed because it was
unused.

* src/ltlast/automatop.cc, src/ltlast/automatop.hh,
src/ltlast/formula_tree.cc, src/ltlast/formula_tree.hh,
src/ltlast/nfa.cc, src/ltlast/nfa.hh: Delete.
* src/ltlast/Makefile.am: Adjust.
* src/ltlast/allnodes.hh, src/ltlast/formula.hh, src/ltlast/predecl.hh,
src/ltlast/visitor.hh, src/ltltest/equals.cc, src/ltltest/ltlrel.cc,
src/ltltest/reduc.cc, src/ltlvisit/clone.cc, src/ltlvisit/clone.hh,
src/ltlvisit/dotty.cc, src/ltlvisit/lbt.cc, src/ltlvisit/mark.cc,
src/ltlvisit/postfix.cc, src/ltlvisit/postfix.hh,
src/ltlvisit/relabel.cc, src/ltlvisit/simplify.cc, src/ltlvisit/snf.cc,
src/ltlvisit/tostring.cc, src/tgba/formula2bdd.cc,
src/tgbaalgos/ltl2taa.cc, src/tgbaalgos/ltl2tgba_fm.cc,
src/tgbaalgos/ltl2tgba_lacim.cc, src/tgbatest/ltl2tgba.cc,
iface/dve2/dve2check.cc: Remove all references to automatop.

* src/eltlparse/.gitignore, src/eltlparse/Makefile.am,
src/eltlparse/eltlparse.yy, src/eltlparse/eltlscan.ll,
src/eltlparse/fmterror.cc, src/eltlparse/parsedecl.hh,
src/eltlparse/public.hh, src/eltltest/.gitignore,
src/eltltest/Makefile.am, src/eltltest/acc.cc, src/eltltest/acc.test,
src/eltltest/defs.in, src/eltltest/nfa.cc, src/eltltest/nfa.test,
src/tgbaalgos/eltl2tgba_lacim.cc, src/tgbaalgos/eltl2tgba_lacim.hh,
src/tgbatest/eltl2tgba.test: Delete these files.
* src/Makefile.am, src/tgbaalgos/Makefile.am, src/tgbatest/Makefile.am,
src/tgbatest/ltl2tgba.cc, src/tgbatest/ltlcross.test,
src/tgbatest/spotlbtt.test, README, configure.ac: Adjust.

* src/tgbaalgos/dtbasat.cc, src/tgbaalgos/dtbasat.hh,
src/tgbaalgos/dtgbasat.cc, src/tgbaalgos/dtgbasat.hh: Use tgba_digraph
and modernize syntax slightly.

* src/tgbaalgos/emptiness.cc, src/tgbaalgos/emptiness.hh: Use
tgba_digraph instead of tgba_explicit_string.

* src/priv/accmap.hh (acc_mapper): Rename into...
(acc_mapper_string): ... this, and add
(acc_mapper_int): ... this variant.
* src/tgbaparse/tgbaparse.yy: Adjust to renaming.
* src/tgbaalgos/lbtt.cc: Use acc_mapper_int and build an explicit
automaton.
* src/tgbaalgos/lbtt.hh: Adjust return type.
* src/tgbatest/ltl2tgba.cc: Adjust to new return type.

* src/misc/common.hh (SPOT_UNIMPLEMENTED, SPOT_UNREACHABLE,
SPOT_UNREACHABLE_BUILTIN): New macros.
* src/bin/dstar2tgba.cc, src/bin/ltlcross.cc,
src/dstarparse/dstar2tgba.cc, src/eltlparse/eltlparse.yy,
src/ltlast/binop.cc, src/ltlast/bunop.cc, src/ltlast/constant.cc,
src/ltlast/formula_tree.cc, src/ltlast/multop.cc, src/ltlast/nfa.cc,
src/ltlast/unop.cc, src/ltlvisit/dotty.cc, src/ltlvisit/lbt.cc,
src/ltlvisit/lunabbrev.cc, src/ltlvisit/mark.cc,
src/ltlvisit/randomltl.cc, src/ltlvisit/simpfg.cc,
src/ltlvisit/simplify.cc, src/ltlvisit/snf.cc, src/ltlvisit/tostring.cc,
src/misc/intvcomp.cc, src/misc/minato.cc, src/tgba/bdddict.cc,
src/tgba/formula2bdd.cc, src/tgba/tgbasafracomplement.cc,
src/tgbaalgos/eltl2tgba_lacim.cc, src/tgbaalgos/ltl2taa.cc,
src/tgbaalgos/ltl2tgba_fm.cc, src/tgbaalgos/ltl2tgba_lacim.cc,
src/tgbaalgos/simulation.cc, src/tgbatest/ltl2tgba.cc:  Use them.
* src/sanity/style.test: Catch assert(0) and assert(!"text");

* src/graph/graph.hh (new_states): Call reserve().
* src/tgbaalgos/randomgraph.cc: Use tgba_digraph
instead of tgba_string_explicit.

* src/tgbaparse/parsedecl.hh, src/tgbaparse/public.hh,
src/tgbaparse/tgbaparse.yy: Adjust to return a tgba_digraph.
* src/priv/accmap.hh: New file to help creating acceptance
conditions from strings.
* src/priv/Makefile.am: Add accmap.hh
* src/tgba/tgbagraph.hh (tgba_digraph::named_t): New typedef.
* wrap/python/spot.i: Declare that tgba_digraph inherits from tgba.
* src/tgbatest/complementation.cc, src/tgbatest/explpro2.test,
src/tgbatest/explpro3.test, src/tgbatest/explpro4.test,
src/tgbatest/explprod.cc, src/tgbatest/explprod.test,
src/tgbatest/ltl2tgba.cc, src/tgbatest/maskacc.cc,
src/tgbatest/maskacc.test, src/tgbatest/mixprod.cc,
src/tgbatest/powerset.cc, src/tgbatest/randtgba.test,
src/tgbatest/readsave.test, src/tgbatest/tgbaread.cc,
src/tgbatest/tgbaread.test, src/tgbatest/tripprod.cc,
src/tgbatest/tripprod.test: Adjust to the change.

* src/ltlenv/declenv.cc, src/ltlenv/declenv.hh,
src/ltlenv/defaultenv.cc, src/ltlenv/defaultenv.hh,
src/ltlenv/environment.hh, src/tgbaalgos/compsusp.cc: Declare name as
const.

* src/bdd.h, src/cppext.cxx: Handle bddtrue and bddfalse using
special types.

* src/tgbaalgos/dtgbasat.cc, src/tgbaalgos/eltl2tgba_lacim.cc,
src/tgbaalgos/simulation.cc, src/tgbaalgos/tau03opt.cc: Fix
cases where bddtrue and bddfalse where used in a ternary operator.
* src/sanity/style.test: Allow bdd_true()/bdd_false() to be
used in ternary operators.

* src/tgbaalgos/sccinfo.cc, src/tgbaalgos/sccinfo.hh: Implement
the acc_filter_simplify filter, and generalize composition to
be n-ary.
* src/tgbaalgos/sccfilter.cc (used_acc): New method.

The new version currently supports removal of useless state as well as
removal of acceptance sets from non-accepting SCCs (the two versions).
It does not yet support simplifation of acceptance sets and removal of
suspendable formulae.  However the design, using filters that are
composed before being applied, should make it easier to implement.

* src/tgbaalgos/sccfilter.cc, src/tgbaalgos/sccfilter.hh: Implement
the new scc_filter and supporting classes.
* src/tgbaalgos/simulation.cc, src/tgbaalgos/simulation.hh: Use it.
The simulation now always return a tgba_digraph.
* src/tgbatest/sim.test: Adjust.

* src/tgbaalgos/simulation.cc: Buid a tgba_digraph as the result of the
simulation.
* src/tgba/tgbagraph.hh (create_namer): New function.
* src/tgbatest/basimul.test: Add an additional test case that caused a
bug fixed in a previous patch.
* src/tgbatest/sim.test: Adjust.

* src/graph/ngraph.hh (alias_state): New method.
* src/graphtest/ngraph.cc: Use it.

* src/graph/graph.hh: Add some framework to erase transitions, and
defrag the resulting transitions_ vector on demand.  Also remove
the nb_states() and nb_transitions() because num_states() and
num_transitions() already exist.
* src/graphtest/graph.cc, src/graphtest/ngraph.cc: Adjust to
use num_states().
* src/tgba/tgbagraph.hh (merge_transitions): New method.
* src/misc/hash.hh: Add a pair_hash class, needed by
merge_transitions().
* src/graphtest/tgbagraph.cc, src/graphtest/tgbagraph.test: Add states
for transitions removal and merge_transitions().

* src/tgbaalgos/sccfilter.cc,
src/tgbaalgos/sccfilter.hh (scc_filter_states): New overload taking
a tgba_digraph and some scc_info.

* src/graph/graph.hh (trans_iterator): Add operator->() and operator
bool().
* src/tgbaalgos/sccinfo.cc, src/tgbaalgos/sccinfo.hh: New files.
* src/tgbaalgos/Makefile.am: Add them.
* src/tgbatest/ltl2tgba.cc: Use the new dump_scc_info_dot() function.

* src/tgbaalgos/dupexp.cc, src/tgbaalgos/dupexp.hh: Return the
association between new states and old states in a vector instead of a
map.
* src/tgbaalgos/simulation.cc: Adjust.

* src/graph/graph.hh (new_states): New.
* src/tgba/tgbagraph.hh (graph_t): Make it public.
* src/tgbaalgos/simulation.cc: Get read of the acc_compl_automaton
class and replace it by a loop over all states of a tgba_digraph.
Remove some useless data structures.

* src/tgbaalgos/dupexp.cc, src/tgbaalgos/dupexp.hh: Produce
a tgba_digraph instead of a tgba_explicit_number.
* src/tgbaalgos/simulation.cc: First pass to adjust to the use of
tgba_digraph as a return of tgba_dupexp_dfs() and tgba_dupexp_bfs().
Some maps have been replaced by vectors because states are indexed,
but more simplifications could be done.

* src/tgba/tgbagraph.hh: New file.
* src/tgba/Makefile.am: Add it.
* src/graph/graph.hh: Add methods needed by tgbagraph.hh.
* src/graphtest/tgbagraph.cc, src/graphtest/tgbagraph.test: New files.
* src/graphtest/Makefile.am: Add them.

* src/graph/graph.hh, src/graph/ngraph.hh: Here.

* src/graph/graph.hh (boxed_label): If State_Data==void, inherit from
std::tuple<> and implement a data() method.
(digraph::state_data): Return by reference.
* src/graphtest/ngraph.cc, src/graphtest/ngraph.test: Test the
case where State_Data implements the spot::state interface.

* src/graph/ngraph.hh: New file.
* src/graph/Makefile.am: Add it.
* src/graphtest/ngraph.cc, src/graphtest/ngraph.test: New files.
* src/graphtest/Makefile.am: Add them

* src/graph/graph.hh, src/graph/Makefile.am, src/graphtest/graph.cc,
src/graphtest/graph.test, src/graphtest/defs.in,
src/graphtest/Makefile.am: New files.
* src/Makefile.am, configure.ac: Add graph/ and graphtest/.
* README: Mention these directories.