Expose meta_window_get_icon_geometry()

Make meta_window_get_icon_geometry() public, so that it can be used
to from plugins to animate windows minimizing to the correct
position.

Based on a patch from Cosimo Cecchi <cosimoc@gnome.org>

http://bugzilla.gnome.org/show_bug.cgi?id=571109

src/include/window.h

@@ -99,5 +99,7 @@ void meta_window_configure_notify (MetaWindow *window, XConfigureEvent *event);
 const char *meta_window_get_role (MetaWindow *window);
 MetaStackLayer meta_window_get_layer (MetaWindow *window);
 MetaWindow* meta_window_find_root_ancestor    (MetaWindow *window);
+gboolean meta_window_get_icon_geometry (MetaWindow    *window,
+                                        MetaRectangle *rect);
 
 #endif