Bug 742444 - Rejigger unsafeWindow definition to not rely on passing waivers across origins. r=gabor
Bug 742444 - Pass the old wrapper or value to the prewrap callback instead of its flags. r=gabor

We need this so that we can reason about the origin of the wrapper that
previously had a waiver and decide whether or not to extend it.
Bug 742444 - Only propagate waivers between same-origin compartments. r=gabor