This is a huge patch.  tgba_digraph are equiped with some boolean
properties that can be used to indicate whether they represent SBA
(and will carry more informations later).  All algorithms that produce
or use sba_explicit_* automata are changed to use tgba_digraph.
postproc has been rewritten using only tgba_digraph, and this required
changing the return types of many algorithms from tgba* to
tgba_digraph*.

* src/bin/dstar2tgba.cc, src/bin/ltlfilt.cc, src/dstarparse/dra2ba.cc,
src/dstarparse/dstar2tgba.cc, src/dstarparse/nra2nba.cc,
src/dstarparse/nsa2tgba.cc, src/dstarparse/public.hh,
src/tgba/tgbagraph.hh, src/tgba/tgbasafracomplement.cc,
src/tgbaalgos/compsusp.cc, src/tgbaalgos/compsusp.hh,
src/tgbaalgos/degen.cc, src/tgbaalgos/degen.hh,
src/tgbaalgos/dotty.cc, src/tgbaalgos/minimize.cc,
src/tgbaalgos/minimize.hh, src/tgbaalgos/postproc.cc,
src/tgbaalgos/postproc.hh, src/tgbaalgos/sccfilter.cc,
src/tgbaalgos/sccinfo.cc, src/tgbaalgos/stripacc.cc,
src/tgbaalgos/stripacc.hh, src/tgbaalgos/translate.cc,
src/tgbaalgos/translate.hh, src/tgbatest/ltl2tgba.cc,
wrap/python/spot.i: Update.

* src/tgbaalgos/Makefile.am, src/tgbaalgos/gtec/Makefile.am: Add
$(VISIBILITY_CXXFLAGS).
* src/tgbaalgos/bfssteps.hh, src/tgbaalgos/compsusp.hh,
src/tgbaalgos/cutscc.hh, src/tgbaalgos/cycles.hh,
src/tgbaalgos/degen.hh, src/tgbaalgos/dotty.hh,
src/tgbaalgos/dottydec.hh, src/tgbaalgos/dupexp.hh,
src/tgbaalgos/eltl2tgba_lacim.hh, src/tgbaalgos/emptiness.hh,
src/tgbaalgos/gtec/ce.hh, src/tgbaalgos/gtec/explscc.hh,
src/tgbaalgos/gtec/gtec.hh, src/tgbaalgos/gtec/nsheap.hh,
src/tgbaalgos/gtec/sccstack.hh,
src/tgbaalgos/gtec/status.hh, src/tgbaalgos/gv04.hh,
src/tgbaalgos/isdet.hh, src/tgbaalgos/isweakscc.cc,
src/tgbaalgos/isweakscc.hh, src/tgbaalgos/lbtt.hh,
src/tgbaalgos/ltl2taa.hh, src/tgbaalgos/ltl2tgba_fm.hh,
src/tgbaalgos/ltl2tgba_lacim.hh, src/tgbaalgos/magic.hh,
src/tgbaalgos/minimize.hh, src/tgbaalgos/neverclaim.hh,
src/tgbaalgos/postproc.hh, src/tgbaalgos/powerset.hh,
src/tgbaalgos/projrun.hh, src/tgbaalgos/randomgraph.hh,
src/tgbaalgos/reachiter.hh, src/tgbaalgos/reducerun.hh,
src/tgbaalgos/reductgba_sim.cc, src/tgbaalgos/reductgba_sim.hh,
src/tgbaalgos/replayrun.hh, src/tgbaalgos/rundotdec.hh,
src/tgbaalgos/safety.hh, src/tgbaalgos/save.hh, src/tgbaalgos/scc.hh,
src/tgbaalgos/sccfilter.hh, src/tgbaalgos/se05.hh,
src/tgbaalgos/simulation.hh, src/tgbaalgos/stats.hh,
src/tgbaalgos/stripacc.hh, src/tgbaalgos/tau03.hh,
src/tgbaalgos/tau03opt.hh, src/tgbaalgos/translate.hh: Mark public
symbol with SPOT_API.

* src/tgbaalgos/compsusp.cc, src/tgbaalgos/compsusp.hh: New files.
* src/tgbaalgos/Makefile.am: Add them.
* src/tgbaalgos/sccfilter.cc, src/tgbaalgos/sccfilter.hh: Add option
for suspended labels removal.
* src/tgbatest/ltl2tgba.cc, src/tgbatest/spotlbtt.test: Test it.