MetaClassRegistryChangeEventListener doesn't provide a way to get a reference to the old meta class

There is currently no way to know what the previous meta class was in the case of listening for meta class registry change events. This is because you only get a reference to the class and the new meta class in the event. The event is fired after the meta class is changed as well so you can't even use the class to lookup the old meta class. Please provide a way to get hold of the old meta class.