This fixes a bug where {(a&!a)[=2]} was translated either into an
universal automaton (with simplification turned off) or in an
empty automaton (with simplification turned on).

* src/tgbaalgos/ltl2tgba_fm.cc (ratexp_to_dfa::translate): Trim
the automaton.
(ratexp_to_dfa::succ, ratexp_to_dfa::get_label): Deal with trimed
states.
(ltl_trad_visitor::visit(unop::Closure)): Likewise.
* src/tgbatest/ltl2tgba.test, src/ltltest/reduccmp.test: New test
cases.