fullscreen: Raise window after un-fullscreening.

fullscreen: Raise window after un-fullscreening.

Currently, if a window is un-fullscreened, it ends up behind any windows
which it originally overlapped - even if it was in front of them
in the first place.  I have no expectation that the original stacking
order be preserved, but the current behaviour is certainly surprising.

Just raise the thing and be done with it.