Fix a mismatch in the generated interface type and contextual type for the init(rawValue:) initializer; the former was lacking the '(rawValue:)' label and freaking out SILGen's abstraction lowering. When deriving the body of init(rawValue:), substitute the (interface) raw type into the initializer's context, so that we can successfully compare it to other contextualized types in the body's context. Fixes <rdar://problem/19986886>.
Swift SVN r25775
