Bug 973780 - Expose a wrapper for the internal WeakMap class outside of the engine. r=mccr8,terrence
Bug 973780 - Implement an expando WeakMap on XPCWrappedNativeScope. r=mccr8
Bug 973780 - Hook Xrays up to the new expando map. r=bz
Bug 973780 - Remove Xray expando slot from WNs. r=bz
Bug 973780 - Remove Xray expando slot from new-binding objects. r=bz
Bug 973780 - Don't double-unregister during IDB teardown. r=khuey