This makes dstar2tgba able to produce a minimal WDBA when the input DRA
represent an obligation property.
* src/tgbaalgos/minimize.cc (minimize_obligation): When the
formula is not supplied but the input automaton is deterministic,
complement it to check the result of WDBA minimization.
* src/tgbatest/ltl2dstar.test, src/tgbatest/ltl2dstar2.test: Improve
tests.
* src/bin/dstar2tgba.cc, src/bin/man/dstar2tgba.x: New files.
* src/bin/Makefile.am, src/bin/man/Makefile.am: Add them.
* NEWS: Mention it.
* src/bin/ltl2tgba.cc, src/tgbaalgos/stats.cc, doc/org/ltl2tgba.org:
Rename the %S sequence as %c, for consistency with dstar2tgba.
* src/tgbatest/ltl2dstar.test: Add more tests.
* src/tgbatest/ltl2dstar2.test: New file.
* src/tgbatest/Makefile.am: Add it.
