Replace the constant_term visitor by a flag in the formulae.

* src/ltlast/formula.hh (formula::accepts_eword): New method.
(formula::is.accepting_eword): New flag.
* src/ltlast/formula.cc (print_formula_props): Display the new
property.
* src/ltlast/atomic_prop.cc, src/ltlast/automatop.cc,
src/ltlast/binop.cc, src/ltlast/bunop.cc, src/ltlast/constant.cc,
src/ltlast/multop.cc, src/ltlast/unop.cc: Update
is.accepting_eword as appropriate.
* src/ltltest/consterm.cc, src/tgbaalgos/ltl2tgba_fm.cc: Adjust to
use accepts_eword().
* src/ltlvisit/consterm.cc, src/ltlvisit/consterm.hh: Delete.
* src/ltlvisit/Makefile.am: Remove these files.

src/ltlvisit/Makefile.am

@@ -29,7 +29,6 @@ ltlvisitdir = $(pkgincludedir)/ltlvisit
 ltlvisit_HEADERS = \
   apcollect.hh \
   basicreduce.hh \
-  consterm.hh \
   contain.hh \
   clone.hh \
   destroy.hh \
@@ -51,7 +50,6 @@ noinst_LTLIBRARIES = libltlvisit.la
 libltlvisit_la_SOURCES = \
   apcollect.cc \
   basicreduce.cc \
-  consterm.cc \
   contain.cc \
   clone.cc \
   destroy.cc \