swift234

Generalize some overly conservative type checker and verifier code:
when type checking a reference to an optional requirement (producing 
a dynamic_member_ref), downcast the receiver to the protocol in question
instead of to AnyObject.  At SILGen time, we do an unchecked_ref_cast anyway,
and this is a more general solution to the problem it is trying to solve.



Swift SVN r21515