This patch changes the window manager, the decorator, and the
floating window layouter to propagate the usage of an alpha channel from
the client application to the decorator. This way, the decorator can
paint the decoration elements behind the affected windows, which would
otherwise be skipped.
The window manager provides a nitpicker session interface. In contrast
to the nitpicker server, which leaves the view layout up to the client,
the window manager organizes the views on screen according to a policy
provided by a window layouter. Furthermore, it equips views with window
decorations as provided by a window decorator. Both layouter and
decorator are independent programs.
