two unabbreviate_logic definitions (const and non-const) into a
function that takes a const formula* and return a non-const
formula*. Since formula* is convertible to const formula*, and
the const version of the function just called the non-onst one, it
makes no sense to keep both. Also, it confused Swig.
* src/ltlvisit/nenoform.cc, src/ltlvisit/nenoform.hh: Likewise
for negative_normal_form.
* src/ltlvisit/tunabbrev.cc, src/ltlvisit/tunabbrev.hh: Likewise
for unabbreviate_ltl.
* src/ltlvisit/clone.cc, src/ltlvisit/clone.hh: Likewise for clone.
* src/ltlvisit/destroy.cc, src/ltlvisit/destroy.hh: Likewise
for destroy.
* src/ltlast/atomic_prop.hh: Declare instance_count().
* src/ltlast/binop.hh, src/ltlast/unop.hh, src/ltlast/multop.hh:
Likewise. Also, really inherit for ref_formula this time.
* src/ltlast/atomic_prop.cc, src/ltlast/binop.cc,
src/ltlast/unop.cc, src/ltlast/multop.cc: On destruction, suppress
the instance from the instance map. Implement instance_count().
* src/ltlast/formula.cc, src/ltlast/formula.hh,
src/ltlast/ref_formula.cc, src/ltlast/ref_formula.hh: Add virtual
destructors.
* src/ltlparse/ltlparse.yy: Recover from binary operators with
missing right hand operand (the point is just to destroy the
the left hand operand).
* src/ltltest/equals.cc, src/ltltest/readltl.cc,
src/ltltest/tostring.cc: Destroy used formulae. Make sure
instance_count()s are null are the end.
* src/ltltest/parseerr.test: Adjust expected result, now
that the parser lnows about missing right hand operands.
* src/ltlvisit/destroy.hh, src/ltlvisit/destroy.cc,
src/ltlvisit/postfix.hh, src/ltlvisit/postfix.cc: New files.
* src/ltlvisit/Makefile.am (libltlvisit_la_SOURCES): Add them.
* src/ltlvisit/lunabbrev.cc (Xor, Equiv): Clone formulae
occurring twice in the rewritten expression.
