Right now it's tricky to add hooks and *know* you've defined each proxy handler hook correctly, because omitting a hook from a derived class will silently "work", if a base class defines the hook. And if the base definition isn't good enough, that's (silently) really bad. Additionally, defining hooks through the vtable means we can't form function pointers to them, which it'd be nice to be able to do in the JITs. (There are certain implementation tactics that depend upon this capability, that I think we'll want to do at some point.) So let's convert the vtable to an explicit set of function pointers, for clarity.