extracted from ...
* src/ltlvisit/lunabbrev.cc: ... this one, which now work as documented
again.
* src/ltlvisit/reduce.cc, src/ltlvisit/syntimpl.cc: Adjust to call
simplify_f_g() in addition to unabbreviate_logic().
* src/ltlvisit/Makefile.am (ltlvisit_HEADERS, libltlvisit_la_SOURCES):
Add simpfg.cc and simpfg.hh.