After shift+F11, both in Windows 7 and xp clients, WM_KEYUP events were missing for
SHIFT and F11. For F11 it was less important since unpress_all was preformed for all keys.
However, we perform sync for all the keyboard modifiers and the GetKeyboardState returns "down" for shift.
In windows7 client, we sometimes received afterwards a F11 KEYDOWN event repetition, and this caused SHIFT+F11 to be called again.
Not performing hiding of the windows while changing client resolutions, solved the problem of missing events, and I don't see any difference
in how spice looks while toggling to full screen.
Using GetAsyncKeyState, returns "UP" for shift in windows 7, and helps avoid performing shift+f11 again, if there is an F11 repetition
before we receive the KEYUP event for shift.