The metacity core is now directly aware of override redirect windows.
- They get MetaWindows like normal windows, so mutter no longer need to special
case them. The net wm types applicable to override redirects are also
recognised.
- The original positioning/stacking semantics of metacity with respect to OR
windows are maintained, but now it's easier to synchronize the stacking
between the core and mutter.
- mutter no longer needs to manualy track UnmapNotify, MapNotify,
ReparentNotify, CreateNotify and DestroyNotify events; instead map, unmap,
add and remove events can now be consistently delivered via the
MetaCompositor callbacks.
