Fix so Javascript can call CoreData object properties

[afedor]

Properties of subclassed CoreData objects can't be called from Javascript currently. CoreData uses internal private functions to implement the dynamic properties, and this does not seem to work with the runtime method introspection functions, but they do work with NSObject introspection methods. In this patch I only use the NSObject methods if the runtime functions fail, but it seems like you could use the NSObject methods always.

Includes some Unit Tests that illustrate the problem.