* src/ltlast/automatop.hh, src/ltlast/automatop.cc: Add missing
instance_count() functions.
* src/tgbatests/eltl2tgba.cc: Add missing instance_count()
assertions at the end.
* src/tgbatests/ltl2tgba.cc: Also call automatop::instance_count(),
even if automatop are not used in ltl2tgba yet.  This way we won't
forget once eltl2tgba and ltl2tgba are merged.