* src/ltlvisit/Makefile.am (libltlvisit_a_SOURCES): Add equals.hh
and equals.cc.
* src/ltltest/equals.cc, src/ltltest/equals.test: New files.
* src/ltltest/Makefile.am (check_PROGRAMS): Add equals.
(equals_SOURCES): New variable.
(TESTS): Add equals.test.

(multop::add): If the formulae we add is itself a multop for the
same operator, merge its children with ours.
* src/ltltest/parseerr.test: Add two tests for multop merging.

* src/ltlast/unop.hh (unop::equals): Remove.
* src/ltlast/unop.cc (unop::equals): Remove.
* src/ltlast/binop.hh (binop::equals): Remove.
* src/ltlast/binop.cc (binop::equals): Remove.
* src/ltlast/multop.hh (multop::equals): Remove.
* src/ltlast/multop.cc (multop::equals): Remove.
* src/ltlast/atomic_prop.hh (atomic_prop::equals): Remove.
* src/ltlast/atomic_prop.cc (atomic_prop::equals): Remove.
* src/ltlast/constant.hh (constant::equals): Remove.
* src/ltlast/constant.cc (constant::equals): Remove.

src/Makefile.am, src/ltlast/Makefile.am, src/ltlast/allnodes.hh,
src/ltlast/atomic_prop.cc, src/ltlast/atomic_prop.hh,
src/ltlast/binop.cc, src/ltlast/binop.hh, src/ltlast/constant.cc,
src/ltlast/constant.hh, src/ltlast/formulae.hh,
src/ltlast/multop.cc, src/ltlast/multop.hh, src/ltlast/predecl.hh,
src/ltlast/unop.cc, src/ltlast/unop.hh, src/ltlast/visitor.hh,
src/ltlparse/Makefile.am, src/ltlparse/ltlparse.yy,
src/ltlparse/ltlscan.ll, src/ltlparse/parsedecl.hh,
src/ltlparse/public.hh, src/ltlvisit/Makefile.am,
src/ltlvisit/dotty.cc, src/ltlvisit/dotty.hh,
src/ltlvisit/dump.cc, src/ltlvisit/dump.hh,
src/ltlvisit/rewrite.cc, src/ltlvisit/rewrite.hh,
src/ltltest/Makefile.am, src/ltltest/defs.in, src/ltltest/readltl.cc,
src/ltltest/parse.test, src/ltltest/parseerr.test,
src/misc/Makefile.am, src/misc/const_sel.hh: New files.