late Wayland changes

[Matthias Clasen <matthias clasen gmail com>]

With the scheduling of guadec, .90 and vacations, we missed the boat
with some Wayland related changes that we still want to get into 3.22.

https://bugzilla.gnome.org/show_bug.cgi?id=769936 (mutter)
https://bugzilla.gnome.org/show_bug.cgi?id=769937 (gtk+)
https://bugzilla.gnome.org/show_bug.cgi?id=769669 (gtk+)
https://bugzilla.gnome.org/show_bug.cgi?id=770026 (gtk+)

I hope we can get most of this landed this week.