Better types for instance maps.

* src/ltlast/unop.hh (map): Use unop* as values.
* src/ltlast/binop.hh (map): Use binop* as values.
* src/ltlast/multop.hh (map): Use multop* as values.
* src/ltlast/automatop.hh (paircmp): Rename as tripletcmp.
(map): Use automaton* as values, not formula*.

src/ltlast/multop.hh

@@ -108,7 +108,7 @@ namespace spot
 	  return *p1.second < *p2.second;
 	}
       };
-      typedef std::map<pair, formula*, paircmp> map;
+      typedef std::map<pair, multop*, paircmp> map;
       static map instances;
 
       multop(type op, vec* v);