Conform NSDate to Comparable

[chrisamanse]

No description provided.

[JiriTrecak]

Personally, I think compare function can be shortened so it does not introduce unnecessary overhead, to:

public func <(lhs: NSDate, rhs: NSDate) -> Bool {
    return lhs.timeIntervalSinceReferenceDate < rhs.timeIntervalSinceReferenceDate
}    

[chrisamanse]

@JiriTrecak, good point.

[parkera]

This pull request contains an API change, so let’s follow the Swift evolution process, starting with discussing the idea on the swift-evolution and swift-corelibs-dev lists.