swift234

Make @objc enums that conform to ErrorType also conform to _ObjectiveCBridgeableErrorType.

This allows @objc enum error types produced in Objective-C (e.g., via
+[NSError errorWithDomain:code:userInfo:]) to be bridged back to their
original enum types in Swift via pattern matching/catch blocks.

This finishes rdar://problem/20577517.

Swift SVN r28803