beIdenticalTo can now be used on non NSObject objects

Taking SwiftHamcrests sameInstance-matcher https://github.com/nschum/SwiftHamcrest/blob/master/Hamcrest/BasicMatchers.swift#L5 this removes the constraint that beIdenticalTo could only be used on objects of classes inheriting from NSObject.

__Note that I currently don't have access to a  OS X 10.10 system and so could test it only on iOS.__