Bug#838050: Patched upstream

[Andrew Chadwick]

Apologies for the big messy merge.

Upstream now have a patch for this, currently pending review, which
applies cleanly to Debian mutter 3.21.92-1 and fixes the knock-on
problems in gnome-shell etc.

https://bugzilla.gnome.org/show_bug.cgi?id=771628
https://bugzilla.gnome.org/attachment.cgi?id=335863&action=diff

With my patched local build, all the hardware I've tested now works
and doesn't crash gnome-shell in wayland or xorg.

-- 
Andrew Chadwick