Bug 1034244 - Check only for WN Xrays when deciding whether the prototype is useless. r=mrbkap
Bug 1034244 - Include TypedArrays in SpecialPowers Xray waiving list. r=mrbkap

Our Xrays to TypedArrays basically just say "this will be slow - clone instead".
Let's just have SpecialPowers waive Xrays for them to make things work less
surprisingly.
Bug 1034244 - Follow the prototype chain of the underlying object in SpecialPowers wrapping. r=mrbkap
Bug 1034244 - Hoist SpecialPowers Xray waiving into a separate function so that we can apply it at each stage when climbing the prototype chain. r=mrbkap