gdkwindow: Handle updates created by outstanding moves in same update

gdkwindow: Handle updates created by outstanding moves in same update

If gdk_window_flush_outstanding_moves() creates new update area
we handle this directly in the same draw to avoid flashing.

This mainly affects win32 as X11 does its exposes from moves async.
However, its important for win32 since ScrollDC seems to sometimes
invalidate (and not copy) unexected regions.

http://bugzilla.gnome.org/show_bug.cgi?674051