swift234

Map user/library-level redefinitions of id, Class, and SEL in Objective-C to their built-in equivalents.

This makes sure that, when we load the real Foundation module, all
references to id/Class/SEL get mapped to NSObject/NSObject/ObjCSel.

Note that you'll need Clang r174234 for this to actually work
properly. Clang modules weren't coping with these redefinitions
appropriately.


Swift SVN r3934