To keep feature parity with the Wayland backend, and to improve the overall tiling experience with GTK apps, add the _GTK_EDGE_CONSTRAINTS X11 atom and update it when necessary. https://bugzilla.gnome.org/show_bug.cgi?id=751857
Implement _NET_RESTACK_WINDOW, based on metacity commit 0b5a50c8. Also respect "above" field (sibling) of XConfigureRequestEvent. When it is set, perform a stack operation relative to that sibling. https://bugzilla.gnome.org/show_bug.cgi?id=786363 https://bugzilla.gnome.org/show_bug.cgi?id=786365
This should *not* be part of the public API.