Move NSObject extensions to the ObjectiveC overlay
Move NSObject extensions to the ObjectiveC overlay

NSObject is defined in the ObjectiveC module, not in Foundation.

rdar://20526438

Swift SVN r28591

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation