metacity should support _UNITY_NET_WORKAREA_REGION

Binary package hint: metacity

I'm copy-paste the explanation by Sam Spilsbury:
_NET_WORKAREA_REGION x, y, width, height CARDINAL[][4]/32

This property MUST be set by the Window Manager upon calculating the
total workarea region for the currently active desktop. Contains a
series of rectangles describing the area not covered by strut windows.
Work area region SHOULD be used by override redirect windows to ensure
that they position themselves in places that do not occlude struts.

The Window Manager SHOULD calculate this space by taking the currently
active desktop space minus space occupied by dock and panel windows, as
indicated by the _NET_WM_STRUT or _NET_WM_STRUT_PARTIAL properties set
on client windows.

Rationale: Currently, there are cases where override redirect windows
must be able to place themselves in positions that are not occluding
strut windows. With _NET_WORKAREA this is partially possible, but only
tells these clients of a single rect that they can place windows within.
This excludes the cases where there are struts that only partially cover
the screen (eg _NET_WM_STRUT_PARTIAL) or there are struts that cover the
space between multiple monitors (eg a top/bottom case with the Unity
Panel)