Minor changes to gtk2_send_mouse_move() for GTK 2.6

First, it seems that once the mouse is moved, GDK 2.6 will keep sending updates
- even if no movement has occurred. Fix: check for this and return as fast as
possible to avoid hogging the cpu.

Also, GDK now seems able to see XWarpPointer() moves, causing the guest pointer
to be wrapped (if mouse acceleration is off, the guest pointer will be trapped
in the "box"). Fix: manually update the internal mosue position first, so
these moves will look like the "zero moves" above, so we can ignore them.

-- 
Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.