Bug 901116. Give a better error message if the same name is typedeffed twice in WebIDL. r=khuey

We could also switch typedefs to using IDLWrapperType, but this seems like a smaller and still-sane change.

dom/bindings/parser/WebIDL.py

@@ -243,7 +243,7 @@ class IDLScope(IDLObject):
                 return
 
             # ensureUnique twice with the same object is not allowed
-            assert object != self._dict[identifier.name]
+            assert id(object) != id(self._dict[identifier.name])
 
             replacement = self.resolveIdentifierConflict(self, identifier,
                                                          self._dict[identifier.name],