* src/ltlast/automatop.cc, src/ltlast/automatop.hh: Rename nfa as
get_nfa to avoid a name clash with the `nfa' class.
* src/ltlvisit/clone.cc, src/ltlvisit/nenoform.cc,
src/ltlvisit/tostring.cc, src/tgbaalgos/eltl2tgba_lacim.cc: Use
get_nfa instead of nfa.
* src/tgba/tgbasafracomplement.cc: Don't use a
const_reverse_iterator.