This fixes#6.
* src/graph/graph.hh: Rename the old transitions() as
transition_vector(), and implement a new transitions() that iterates
only on non-dead transitions.
* src/tgba/tgbagraph.hh, src/tgba/tgbagraph.cc, src/graph/ngraph.hh:
Adjust wrappers.
* src/hoaparse/hoaparse.yy, src/tgbaalgos/complete.cc,
src/tgbaalgos/dtbasat.cc, src/tgbaalgos/dtgbasat.cc,
src/tgbaalgos/randomize.cc, src/tgbaalgos/safety.cc: Adjust calls.
* src/graph/ngraph.hh (alias_states): Deal with the case
of aliasing two existing states.
* src/hoaparse/hoaparse.yy: Fix handling of aliased states.
* src/tgbatest/neverclaimread.test: Augment test case.
The conversion is not complete, because the conversion from SERE to DRA
used for the closure operator is still building a tgba_explicit_formula.
* src/tgbaalgos/ltl2tgba_fm.cc, src/tgbaalgos/ltl2tgba_fm.hh: Return
a tgba_digraph.
* src/priv/acccompl.cc: Simplify.
* src/graph/ngraph.hh: Add a way to iterate over all names.
* src/tgba/tgbagraph.hh (compute_support_conditions): Return something
useful. It's actually used by the constructor of testing automata.
* src/tgbatest/wdba.test: Adjust to the fact that state are not
labeled by formulas anymore.
* src/bin/ltl2tgba.cc, src/bin/ltl2tgta.cc: Do not try to enable
UTF8 on automata anymore.
* 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
