Generalize implication-based simplifications for multops.

And also speedup implication checks for Boolean expressions.

* src/ltlvisit/simplify.cc: Improve implication-based rules
rules for multops by checking one operand against all the
other at once (instead of one by one).  Do not break
Boolean expressions while performing implication checks.
* src/ltlvisit/simplify.hh: Typo.
* src/ltltest/reduccmp.test: More tests.

src/ltlvisit/simplify.hh

@@ -121,7 +121,7 @@ namespace spot
       ///
       /// If \a right is true, this method returns whether
       /// \a f implies !\a g.  If \a right is false, this returns
-      /// whether !\a g implies \a g.
+      /// whether !\a f implies \a g.
       bool syntactic_implication_neg(const formula* f, const formula* g,
 				     bool right);