* src/twaalgos/ltl2tgba_fm.hh, src/twaalgos/ltl2tgba_fm.cc: Implement
generation of unambiguous automata.
* src/tests/ltl2tgba.cc: Add option -fu to test it.
* src/bin/common_post.cc: Adjust the group of options so we can easily
add more from ltl2tgba.cc.
* src/bin/ltl2tgba.cc: Add support for -U and --unambigous.
* src/twaalgos/translate.cc, src/twaalgos/translate.hh: Add support
for Unambiguous.
* src/tests/ltlcross.test, src/tests/ltlcross2.test: Test both
bin/ltl2tgba and tgbatest/ltl2tgba.
* NEWS: Mention the change.
