This is faster than using the abstract interface, and it also supports
alternating automata.  (This will be tested in the tests for
ltlcross's support for alternating automata.)

* spot/twaalgos/stats.cc (stats_reachable, sub_stats_reachable):
Add code specific to twa_graph_ptr.

* spot/twaalgos/remfin.cc (remove_fin_weak): Ignore unreachable
states.  This caused crashes in the test cases for the
upcoming alternation support in ltlcross.

This mixes the subset construction (for 1-state rejecting SCCs) and
the breakpoint construction (for larger rejecting SCCs).  The
algorithm should probably be rewritten in a cleaner and more efficient
way, but that should do for a first version.  It should be easy to
extend it to support Büchi acceptance (since the breakpoint
construction works for this) when we need it.

* spot/twaalgos/alternation.hh,
spot/twaalgos/alternation.cc (remove_alternation): New function.
* tests/python/alternation.ipynb: New file.
* tests/Makefile.am, doc/org/tut.org: Add it.

* spot/twa/twa.hh: Implement the property.
* spot/parseaut/parseaut.yy, spot/twaalgos/hoa.cc: Add input
and output for it.
* spot/twaalgos/strength.cc,
spot/twaalgos/strength.hh (is_very_weak_automaton): New function.
* tests/core/alternating.test: Add a test for --check=strength
on an alternating automaton.
* tests/core/strength.test, tests/core/parseaut.test: Adjust expected
output.
* NEWS, doc/org/hoa.org, doc/org/concepts.org: Document it.

* spot/twaalgos/sccinfo.cc: Consider universal edges as if they were
existential edges.
* spot/twaalgos/sccinfo.hh: Document that.
* spot/twaalgos/dot.cc: Allow option 's' again, for easy testing.
* tests/core/alternating.test: Adjust tests.
* tests/python/_altscc.ipynb: New file (more tests).
* tests/Makefile.am: Add it.

* spot/parseaut/parseaut.yy (fix_initial_state): Use
spot::internal::outgoing_edge_group to reduce all initial states to a
single one.
* tests/core/parseaut.test: Add more tests.

This should will come handy to implement the convertion from LTL to
alternating automata, and to handle automata with multiple initial
states.

* spot/twaalgos/alternation.hh, spot/twaalgos/alternation.cc: New files.
* spot/twaalgos/Makefile.am: Add them.
* python/spot/impl.i: Add bindings.
* tests/python/alternating.py: Test states_and.

The only missing point is that the HOA parser cannot deal with multiple
universal initial states, as seen in parseaut.test.

* spot/graph/graph.hh (new_univ_dests): New function, extracted from...
(new_univ_edge): ... this one.
* spot/twa/twagraph.hh (set_univ_init_state): Implement using
new_univ_dests.
* spot/twaalgos/dot.cc, spot/twaalgos/hoa.cc, python/spot/impl.i:
Add support for universal initial states.
* spot/parseaut/parseaut.yy: Add preliminary support for
universal initial states.  Multiple universal initial states
are still not supported.
* tests/core/alternating.test, tests/core/parseaut.test,
tests/python/alternating.py: Adjust tests and exercise this new feature.

* spot/twaalgos/dot.cc: Handle universal destinations.
Ignore option 's' for alternating automata.
* tests/core/alternating.test: New file.
* tests/Makefile.am: Add it.

Currently this only reads universal branches.  The parser (and the
automaton code) do not support universal initial states.

* spot/parseaut/parseaut.yy: Read universal branches.  Deal with
the no-univ-branch/!univ-branch change in HOA 1.1.
* tests/python/alternating.py: Read the output of print_hoa.
* tests/core/parseaut.test: Adjust test output, and add more tests.

* spot/twaalgos/hoa.cc: Implement it.
* tests/python/alternating.py: Test it.

This only allows creating universal edges, and reading the associated
destinations.

* spot/twa/twagraph.hh (new_univ_edges, univ_dests, is_alternating): New
function.
* python/spot/impl.i: Add Python bindings.
* tests/python/alternating.py: New file.
* tests/Makefile.am: Add it.

* spot/graph/graph.hh: Use the sign bit of destination state X to
designate a universal edge.  Store the destinations of such an edge in a
separate array, at index ~X.
* spot/graph/ngraph.hh, tests/core/graph.cc, tests/core/graph.test,
tests/core/ngraph.cc: Adjust test case to the new interface.

* doc/org/tut22.org: Here.

* doc/org/ltlcross.org: Also fix the documentation of terminal and
weak SCCs.

* doc/org/.dir-locals.el.in, doc/org/init.el.in: Load "shell" instead
of "sh" for recent org-mode version.

* spot/twaalgos/copy.hh: Make a reference to make_twa_graph().

* spot/twaalgos/strength.hh: Add a verb to the descriptions.
Suggested by Alexandre Gbaguidi Aïsse.

* NEWS, configure.ac: Set version 2.2.2.dev.

* NEWS, configure.ac, doc/org/setup.org: Update version.

* python/spot/__init__.py (automata): Do not create a session for
every command, this is only needed if automata() is run with a timeout
parameter.
* python/ajax/spotcgi.in: Adjust exclude the main process from
the process group, so that only children are killed on SIGALRM.
* NEWS: Mention the bug.

* python/spot/__init__.py (automata): Do not create a session for
every command, this is only needed if automata() is run with a timeout
parameter.
* python/ajax/spotcgi.in: Adjust exclude the main process from
the process group, so that only children are killed on SIGALRM.
* NEWS: Mention the bug.

* configure.ac: add an option --enable-c++14.
* NEWS: mention the new option.

* configure.ac: add an option --enable-c++14.

* spot/twa/twa.cc: is_empty() and accepting_run() now call the new
version of the Couvreur algorithm.

This version has optimization for explicit twa, and also for weak and
terminal (depending on whether an accepting run is requested) automata.

* spot/twaalgos/couvreurnew.hh, spot/twaalgos/couvreurnew.cc,
  spot/twaalgos/Makefile.am: New files for the new algorithm.
* spot/twaalgos/emptiness.cc, tests/core/randtgba.cc:
  Register new algorithm.

* spot/ltsmin/ltsmin.cc: Add an assert.

Reported by Shufang Zhu.

* spot/tl/ltlf.cc, spot/tl/ltlf.hh: Fix the transltion
and update the comments.
* tests/core/ltlfilt.test: Adjust test cases.
* NEWS: Mention the fix.
* THANKS: Add Shufang Zhu.

Reported by Shufang Zhu.

* spot/tl/ltlf.cc, spot/tl/ltlf.hh: Fix the transltion
and update the comments.
* tests/core/ltlfilt.test: Adjust test cases.
* NEWS: Mention the fix.
* THANKS: Add Shufang Zhu.

Compilation of each header file alone, as a safety check, was removed
when introducing "#pragma once" because we did not have to check for
possible double inclusion.  However we still need to compile each
header to make sure they are self-contained.

* tests/sanity/includes.test: Compile each header.
* tests/run.in: Export various compiler and directory flags.
* spot/twaalgos/emptiness_stats.hh, spot/misc/mspool.hh,
spot/misc/fixpool.hh: Include <spot/misc/common.hh>.
* spot/misc/common.hh: Include <cassert>.
* NEWS: Mention the fixed headers.

Compilation of each header file alone, as a safety check, was removed
when introducing "#pragma once" because we did not have to check for
possible double inclusion.  However we still need to compile each
header to make sure they are self-contained.

* tests/sanity/includes.test: Compile each header.
* tests/run.in: Export various compiler and directory flags.
* spot/twaalgos/emptiness_stats.hh, spot/misc/mspool.hh,
spot/misc/fixpool.hh: Include <spot/misc/common.hh>.
* spot/misc/common.hh: Include <cassert>.
* NEWS: Mention the fixed headers.

* spot/parseaut/parseaut.yy: Add a diagnostic.
* tests/core/parseaut.test: Test it.
* NEWS: Document it.

This should solve issue with the Debian package.

* spot/ltsmin/Makefile.am: Use the LTDLINC, LTDLDEPS and LIBLTDL as
documented.
* NEWS: Mention the fix.

* spot/parseaut/parseaut.yy: Add a diagnostic.
* tests/core/parseaut.test: Test it.
* NEWS: Document it.

* tests/run.in: Here.

* tests/sanity/style.test: Allow parenthesis after 'operator delete'.