Trim DFAs used when translating PSL's closure operators.

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.

src/ltltest/reduccmp.test

@@ -196,6 +196,12 @@ for x in ../reduccmp ../reductaustr; do
      # Because reduccmp will translate the formula,
      # this also check for an old bug in ltl2tgba_fm.
      run 0 $x '{(c&!c)[->0..1]}!' '0'
+
+     # Tricky case that used to break the translator,
+     # because it was translating closer on-the-fly
+     # without pruning the rational automaton.
+     run 0 $x '{(c&!c)[=2]}' '0'
+
      ;;
   esac