Fixing bug 304423. Make window instanceof Object and Window etc be true again....

Fixing bug 304423. Make window instanceof Object and Window etc be true again. This regressed with the split window landing. The fix here is to make the inner and outer windows share the outer's XPConnect prototype (but only that, everything below that on the proto chain comes from the inner window). To make this work with fastback we also needed a way to tell XPConnect to restore an old prototype for the window object when going back/forward. r=mrbkap@gmail.com, sr=brendan@mozilla.org