* spot/twaalgos/determinize.cc: the acceptance condition
  of the determinized automaton should be simpler
* tests/core/safra.test, tests/python/simstate.py: update tests

* spot/twaalgos/parity.cc: cleanup_parity and cleanup_parity_here are
  now better at finding useless parity colors
* tests/python/parity.py: test it
* NEWS: document the change

This helps working around missing C functions like strcasecmp that do
not exist everywhere (e.g. on Cygwin), and for which lib/ supplies a
replacement.  Unfortunately we do not have such build in our current
continuous integration suite, so we cannot easily detect files where
such config.h inclusion would be useful.  Therefore this patch simply
makes it mandatory to include config.h in *.cc files.  Including this
in public *.hh file is currently forbidden.

* spot/gen/automata.cc, spot/gen/formulas.cc,
spot/kripke/fairkripke.cc, spot/kripke/kripke.cc,
spot/ltsmin/ltsmin.cc, spot/misc/game.cc, spot/parseaut/fmterror.cc,
spot/parsetl/fmterror.cc, spot/parsetl/parsetl.yy,
spot/priv/bddalloc.cc, spot/priv/freelist.cc, spot/priv/satcommon.cc,
spot/priv/trim.cc, spot/priv/weight.cc, spot/ta/ta.cc,
spot/ta/taexplicit.cc, spot/ta/taproduct.cc, spot/ta/tgtaexplicit.cc,
spot/ta/tgtaproduct.cc, spot/taalgos/dot.cc,
spot/taalgos/emptinessta.cc, spot/taalgos/minimize.cc,
spot/taalgos/reachiter.cc, spot/taalgos/statessetbuilder.cc,
spot/taalgos/stats.cc, spot/taalgos/tgba2ta.cc, spot/tl/apcollect.cc,
spot/tl/contain.cc, spot/tl/declenv.cc, spot/tl/defaultenv.cc,
spot/tl/dot.cc, spot/tl/exclusive.cc, spot/tl/hierarchy.cc,
spot/tl/length.cc, spot/tl/ltlf.cc, spot/tl/mark.cc,
spot/tl/mutation.cc, spot/tl/nenoform.cc, spot/tl/print.cc,
spot/tl/randomltl.cc, spot/tl/relabel.cc, spot/tl/remove_x.cc,
spot/tl/simplify.cc, spot/tl/snf.cc, spot/tl/unabbrev.cc,
spot/twa/acc.cc, spot/twa/bdddict.cc, spot/twa/bddprint.cc,
spot/twa/formula2bdd.cc, spot/twa/taatgba.cc, spot/twa/twa.cc,
spot/twa/twagraph.cc, spot/twa/twaproduct.cc, spot/twaalgos/aiger.cc,
spot/twaalgos/alternation.cc, spot/twaalgos/are_isomorphic.cc,
spot/twaalgos/bfssteps.cc, spot/twaalgos/canonicalize.cc,
spot/twaalgos/cleanacc.cc, spot/twaalgos/cobuchi.cc,
spot/twaalgos/complement.cc, spot/twaalgos/complete.cc,
spot/twaalgos/compsusp.cc, spot/twaalgos/couvreurnew.cc,
spot/twaalgos/cycles.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/dot.cc,
spot/twaalgos/dtbasat.cc, spot/twaalgos/dtwasat.cc,
spot/twaalgos/dualize.cc, spot/twaalgos/emptiness.cc,
spot/twaalgos/gtec/ce.cc, spot/twaalgos/gtec/gtec.cc,
spot/twaalgos/gtec/sccstack.cc, spot/twaalgos/gtec/status.cc,
spot/twaalgos/gv04.cc, spot/twaalgos/hoa.cc,
spot/twaalgos/iscolored.cc, spot/twaalgos/isdet.cc,
spot/twaalgos/isunamb.cc, spot/twaalgos/isweakscc.cc,
spot/twaalgos/langmap.cc, spot/twaalgos/lbtt.cc,
spot/twaalgos/ltl2taa.cc, spot/twaalgos/ltl2tgba_fm.cc,
spot/twaalgos/magic.cc, spot/twaalgos/mask.cc,
spot/twaalgos/minimize.cc, spot/twaalgos/neverclaim.cc,
spot/twaalgos/parity.cc, spot/twaalgos/postproc.cc,
spot/twaalgos/powerset.cc, spot/twaalgos/product.cc,
spot/twaalgos/rabin2parity.cc, spot/twaalgos/randomgraph.cc,
spot/twaalgos/randomize.cc, spot/twaalgos/reachiter.cc,
spot/twaalgos/relabel.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/remprop.cc, spot/twaalgos/sbacc.cc,
spot/twaalgos/sccfilter.cc, spot/twaalgos/sccinfo.cc,
spot/twaalgos/se05.cc, spot/twaalgos/sepsets.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/split.cc,
spot/twaalgos/stats.cc, spot/twaalgos/strength.cc,
spot/twaalgos/stripacc.cc, spot/twaalgos/stutter.cc,
spot/twaalgos/sum.cc, spot/twaalgos/tau03.cc,
spot/twaalgos/tau03opt.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/toweak.cc, spot/twaalgos/translate.cc,
spot/twaalgos/word.cc, tests/core/acc.cc, tests/core/bitvect.cc,
tests/core/checkpsl.cc, tests/core/checkta.cc, tests/core/consterm.cc,
tests/core/emptchk.cc, tests/core/equalsf.cc, tests/core/graph.cc,
tests/core/ikwiad.cc, tests/core/intvcmp2.cc, tests/core/intvcomp.cc,
tests/core/kind.cc, tests/core/kripkecat.cc, tests/core/length.cc,
tests/core/ltlrel.cc, tests/core/ngraph.cc, tests/core/parity.cc,
tests/core/randtgba.cc, tests/core/readltl.cc, tests/core/reduc.cc,
tests/core/safra.cc, tests/core/sccif.cc, tests/core/syntimpl.cc,
tests/core/taatgba.cc, tests/core/tostring.cc, tests/core/trival.cc,
tests/core/twagraph.cc, tests/ltsmin/modelcheck.cc,
spot/parseaut/scanaut.ll, spot/parsetl/scantl.ll: Include config.h.
* spot/gen/Makefile.am, spot/graph/Makefile.am,
spot/kripke/Makefile.am, spot/ltsmin/Makefile.am,
spot/parseaut/Makefile.am, spot/parsetl/Makefile.am,
spot/priv/Makefile.am, spot/ta/Makefile.am, spot/taalgos/Makefile.am,
spot/tl/Makefile.am, spot/twa/Makefile.am, spot/twaalgos/Makefile.am,
spot/twaalgos/gtec/Makefile.am, tests/Makefile.am: Add the -I lib/
flags.
* tests/sanity/includes.test: Catch missing config.h in *.cc, and
diagnose config.h in *.hh.
* tests/sanity/style.test: Better diagnostics.

* NEWS, configure.ac: Here.

* NEWS, configure.ac, doc/org/setup.org: Set version to 2.5.1.

* doc/org/install.org: Point to the gitlab-ci artefacts.

The bug is mentioned by Maximilien Colange in a comment to issue #317,
but turned out to be unrelated to that original issue.

* spot/twaalgos/totgba.cc (dnf_to_streett): Save the correspondence
between the created states an the DNF clause in a named property.
* doc/org/concepts.org, spot/twaalgos/totgba.hh: Mention the new
property.
* spot/twaalgos/cobuchi.cc (save_inf_nca_st): Rewrite using the named
property.  Relying on seen marks and trying to deduce the matching
original clause could only work from plain Rabin.
* tests/core/dca.test: Add the test from Maximilien.
* NEWS: Mention the issue.

* spot/twaalgos/cobuchi.cc, spot/twaalgos/totgba.cc: Here.

Fixes #324, reported by Tobias Meggendorfer and František Blahoudek.

* spot/twa/acc.hh (rs_pairs_view::paired_with): Rename as...
(rs_pairs_view::paired_with_fin):... this and adjust the code.
* spot/twaalgos/remfin.cc: Use paired_with_fin instead of
paired_with, and do it once per pair.
* tests/core/remfin.test: Add a test case.
* NEWS: Mention the issue.

* spot/twaalgos/cleanacc.cc (merge_identical_marks_here): Do not call
cleanup_acceptance_here(), as this has already been done.

Fixes #325.

* spot/twa/acc.cc: Here.
* tests/core/accsimpl.test: New test case.
* NEWS: Mention the issue.

* tests/python/otfcrash.py: Remove the file generated by divine.

spot::iar() was fixed to handle correctly Rabin-like conditions.
It also now supports Streett-like conditions.

* NEWS, spot/twaalgos/postproc.cc: document it
* spot/twaalgos/rabin2parity.cc, spot/twaalgos/rabin2parity.hh:
  implement it
* tests/core/rabin2parity.test, tests/python/except.py: test it

Fixes #320.

* spot/twaalgos/totgba.cc: Fix the bug.
* NEWS: Mention the problem.
* tests/core/streett.test: Add test case.

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

* tests/python/ipnbdoctest.py: Adjust to Python <3.6.
* tests/python/_autparserr.ipynb: Adjust to older IPython version.
* tests/python/stutter-inv.ipynb: Avoid pandas because its output
varies from version to version.

* python/spot/impl.i: Add missing bindings from remprop.hh
* tests/python/except.py: New file to test several error cases.
* tests/Makefile.am: Add it.
* spot/twaalgos/rabin2parity.cc (iar): Fix error message.

* spot/tl/hierarchy.cc: Here.

* spot/twaalgos/totgba.cc: Here.

* spot/twaalgos/cobuchi.cc: Add scc_info_options::TRACK_SUCCS in
nsa_to_nca().
* spot/twaalgos/sccinfo.cc: Add scc_info_options::TRACK_SUCCS and
is_useful_scc() in states_on_acc_cycle_of().

* spot/twaalgos/cobuchi.cc: Avoid the product of an automaton A and its
power construction Pow(A) when A is deterministic.

* NEWS: Update.
* spot/tl/hierarchy.cc: Replace rabin_to_buchi_maybe() with
is_buchi_realizable().
* spot/twaalgos/remfin.cc: Implement it.
* spot/twaalgos/remfin.hh: Declare it.

* spot/tl/hierarchy.cc: Factorisations, improvements.
* spot/twaalgos/totgba.cc:  Typos.

* spot/twaalgos/sccinfo.cc: Here.

This introduce some section for acceptance transformation, and add
more comments in a few places.

* spot/taalgos/emptinessta.hh, spot/twa/twa.hh, spot/twa/twagraph.hh,
spot/twaalgos/bfssteps.hh, spot/twaalgos/cleanacc.hh,
spot/twaalgos/degen.hh, spot/twaalgos/dualize.hh,
spot/twaalgos/parity.hh, spot/twaalgos/rabin2parity.hh,
spot/twaalgos/remfin.hh, spot/twaalgos/sccinfo.hh,
spot/twaalgos/sepsets.hh, spot/twaalgos/split.hh,
spot/twaalgos/totgba.hh: More doxygen.
* spot/twa/twagraph.cc: Typos in comments.

* spot/twaalgos/rabin2parity.cc, spot/twaalgos/rabin2parity.hh:
  implement it
* spot/twaalgos/postproc.cc: use it
* spot/twaalgos/Makefile.am: build the new files
* NEWS: document the new function
* python/spot/impl.i: Python bindings for the new function
* tests/Makefile.am, tests/core/rabin2parity.test: test the new function

* spot/twaalgos/degen.cc: typo in an error message
* NEWS: fix typos and remove duplicates

* spot/twaalgos/product.hh, spot/twaalgos/remfin.hh,
spot/twaalgos/sum.hh, spot/twaalgos/totgba.hh: Improve documentation.

* spot/twaalgos/cobuchi.cc: Call sbacc() on transition-based input.
* tests/Makefile.am: Remove XFAIL_TESTS.
* NEWS: Adjust.

* spot/twaalgos/cobuchi.cc, spot/twaalgos/cobuchi.hh (to_nca): New
function.
(weak_to_cobuchi): New internal function, used in to_nca and to_dca
when appropriate.
* spot/twaalgos/postproc.cc, spot/twaalgos/postproc.hh: Implement
the CoBuchi option.
* python/spot/__init__.py: Support it in Python.
* bin/common_post.cc: Add support for --buchi.
* bin/autfilt.cc: Remove the --dca option.
* tests/core/dca.test, tests/python/automata.ipynb: Adjust and add
more tests.  In particular, add more complex persistence and
recurrence formulas to the list of dca.test.
* tests/python/dca.test: Adjust and rename to...
* tests/core/dca2.test: ... this.  Add more tests, to the point
that this is now failing, as described in issue #317.
* tests/python/dca.py: Remove.
* tests/Makefile.am: Adjust.

Fixes #316.

* spot/twaalgos/totgba.cc: Fix confusing definition of scc_inf_wo_fin.
* tests/python/streett_totgba2.py: New test case.
* tests/Makefile.am: Add it.
* NEWS: Mention the bug.

We had new failure on MinGW with GCC believing that some pointer
returned by down_cast could be NULL; and the down_cast function was in
the global namespace.

* spot/misc/casts.hh: Rewrite.
* NEWS: Mention the small issues.
* tests/core/ikwiad.cc, tests/core/ngraph.cc: Adjust to use
spot::down_cast instead of down_cast.