This should fix spurious BadWindow errors from the video displays.
(cherry-picked from commit 1c201d48)

There has been a few X11 error crash reports against 1.0, though I do
not know if this will fix them (could be another problem). Basically,
XFlush() is insufficient, as it does not ensure that the X server has
processed the requests.

Conflicts:

	modules/gui/qt4/components/interface_widgets.cpp