* src/bin/common_aoutput.cc: Add --check=unambiguous.
* src/twa/twa.hh: New unambiguous property.
* src/twaalgos/hoa.cc: Print it.
* src/twaalgos/ltl2tgba_fm.cc: Set it.
* src/twaalgos/isunamb.cc, src/twaalgos/isunamb.hh
(check_unambiguous): New function.
* src/tests/unambig.test: More tests.
* src/twaalgos/isunamb.hh, src/twaalgos/isunamb.cc: New files.
* src/twaalgos/Makefile.am: Add them.
* src/tests/unambig.test: New file.
* src/tests/Makefile.am: Add it.
* src/bin/ltlcross.cc: Record whether each produced automaton is
ambiguous.
* src/bin/autfilt.cc: Add a --is-unambiguous option.
* NEWS: Mention it.
