Upcasting `T: Message` to `AnyObject`

[madsmtm]

If all you know about a type is that it is T: Message (or T: ClassType), then you can't safely get AnyObject from that. Probably a rare case, usually you're working with a concrete type, and then you'll simply be able to .as_ref() or deref to it, but would be nice to have.

Maybe it would make sense to add a fn as_any(&self) -> &AnyObject where Self: 'static to Message?

[madsmtm]

Alternatively, we add a Message: AsRef<AnyObject> bound?

But upcasting to AnyObject is only safe if T: 'static, so that probably wouldn't be desirable (then again, objects are already effectively limited to being 'static, so maybe it doesn't matter that much if we actually require it?)