I know you changed to using a hash indexed by class at my suggestion...but I just realized that there's a bug lurking here: when you use `any_instance` on a superclass, and then have an instance of a subclass, this won't work.

To work properly with this mechanism we'd have to index each object by all the modules in its ancestor chain...and that sounds messy.  I think I'd rather it go back to how it was (where you iterated over all proxies looking for matching ones).

Thoughts?