swift234

Following up on r14651, begin flagging and raising an error on indirectly self-recursive protocol requirements.  (This addresses rdar://problem/16081342.)

Admittedly, the error reporting in this area isn't great - it will need to be addressed holistically as part of rdar://problem/16007230.  Still, these changes prevent the compiler from crashing and points to the source of the recursive declaration, leaving some breadcrumbs for users to follow.

Swift SVN r14933