Fixing this bug alone revealed another bug: parsing never claim or LBTT
automata did not register APs. So this fixes both bugs.
This is the first part of #170.
* spot/twa/twa.hh (register_aps_from_dict): New method.
* spot/parseaut/parseaut.yy: Call it for never claim and LBTT files.
* spot/twaalgos/stats.cc: Simplify using ap_vars().
* tests/core/ltl2tgba.test: Add a test case.
* NEWS: Mention the bugs.
* bin/common_aoutput.hh, bin/common_aoutput.cc,
bin/ltl2tgba.cc, bin/ltldo.cc: Add support for %< and %>.
* tests/core/ltl2tgba.test, tests/core/ltldo.test: Test it.
* NEWS: Mention it.