* src/ltlast/formula_tree.cc (instanciate, arity): Add a useless

return 0 at the end to prevent g++ 4.2.3 from complaining about
a missing return.  Reported by Denis Poitrenaud.

src/ltlast/formula_tree.cc

@@ -58,6 +58,7 @@ namespace spot
 
 	/* Unreachable code.  */
 	assert(0);
+	return 0;
       }
 
       size_t
@@ -82,6 +83,7 @@ namespace spot
 
 	/* Unreachable code.  */
 	assert(0);
+	return 0;
       }
     }
   }