Adding things to Object.prototype breaks xdomain loading

[James Burke]

If some other code adds something to Object.prototype, xd loading breaks since it is using an object as a hashmap to find modules that are still being loaded.

While other things in the toolkit may break if someone is bad and modifies Object.prototype, I would like xdomain loading to still work.

[James Burke]

(In [10838]) Fixes #3944. Prevent bad code that adds things to Object.prototype to cause errors in xdomain loading. Not bullet-proof, if an Object.prototype property is added that is a boolean true, xd loading will fail, but hey, don't do that to Object.prototype.