This is about 50% of the way towards making

This is about 50% of the way towards making
_fix_metaclass_incompatibility smart enough to detect when two
metaclass classes differ only in the roles they do.

It works as far as it goes but to do it right it'd have to check and
reconcile the attribute, method, & instance metaclasses, plus the
constructor and destructor class.

All in all, it's a mess.

I'm checking this in to record it, and will rever in the next commit.