This patch emulates motion hints on the client side instead of selecting for
them on the server.

This is needed for getting global motion events, which would be done by
selecting for motion events on all windows. If some windows have motion hints
selected and nobody calls QueryPointer, motions would not be generated.

I am not totally happy with this patch as it selects for crossing, button and
key events, then filters them away if the application didn't actually select for
them. It has to be done this way though, as the X server resets the 'don't
generate motion hints' when those events are generated.