swift234

[Foundation] Ensure _SwiftNSCharacterSet overrides all abstract methods on NSCharacterSet via @objc

The override methods were not marked with @objc which incorrectly funneled to the abstract base class methods. In the method isSuperset(of:) it would incorrectly hit a requirement of a subclass implementation. This exposed a flaw with NSCharacterSet in which that method cannot recieve subclasses to the other CharacterSet being passed. This is being tracked via rdar://problem/27768939 which will need to be accounted for by CoreFoundation. Until such a time that can be addressed the workaround by using CFCharacterSetIsSupersetOfSet must be used with a copy passed as the other set.

This resolves:
https://bugs.swift.org/browse/SR-2307