If mutter_plugin_set_stage_input_region() and related methods are
called before the output window is available, save the set input
region and apply it to the output window later on.
compository-mutter.[ch]: Add mutter_set_stage_input_region() and
mutter_empty_stage_input_region(), move the input region handling
here and implement the delayed shape setting described
above.
mutter-plugin.c: Implement shape setting in terms of the new methods.
http://bugzilla.gnome.org/show_bug.cgi?id=580042
7a7632fa98
