Support _NET_FRAME_EXTENTS.
This patch adds support for the _NET_FRAME_EXTENTS property as
described in the EWMH spec. With it I was able to use the compton
compositing manager to draw fully opaque windows with semi-transparent
titlebars and resizebars.
Set the _NET_FRAME_EXTENTS property based on border widths and
titlebar/resizebar heights.
The EWMH spec says:
"_NET_FRAME_EXTENTS, left, right, top, bottom, CARDINAL[4]/32
The Window Manager MUST set _NET_FRAME_EXTENTS to the extents of the
window's frame. left, right, top and bottom are widths of the
respective borders added by the Window Manager."