swift234

Change RawRepresentable to use failable initializers and property requirements.

Redefine the RawRepresentable protocol to use an 'init?' method instead of 'fromRaw(Raw)', and a 'raw' get-only property instead of 'toRaw()'. Update the compiler to support deriving conformances for enums and option sets with the new protocol. rdar://problem/18216832

Swift SVN r21762