QT should use _NET_FRAME_EXTENTS X property when getting window frame size on X11 whenever possible

I'm running Qt 4.3.4 on Fedora Linux 9, using gcc 4.3.0. Qt is
configured to be run on X11.

The issue is that the internal implementation of QWidget for X11 tries
to walk the window chain upwards until it reaches the root window to
retrieve the size of the window manager frame. Thus, it implicitly
assumes that the window manager reparents the client window (created by
Qt) into the frame, which is true for most, but not all window managers
(e.g. Compiz does not reparent).

Better, IMO, would be trying to use the _NET_FRAME_EXTENTS window
property
(http://standards.freedesktop.org/wm-spec/wm-spec-latest.html#id2552416)
if possible and use that if it's set. If it's not set, fall back to the
window chain walking code.

I've attached a patch which does exactly what I just described - please
consider applying it.