This uses David Herrmann's new logind sessions interface to retrieve
fds for input devices, rather than using a custom setuid helper to do
the management. This vastly simplifies the interface.
This requires systemd v210, at least.
https://bugzilla.gnome.org/show_bug.cgi?id=724604
Move the option from the mutter binary to libmutter, and
rename from --nested to --wayland.
This allows gnome-shell to drop the set_is_wayland_compositor()
call.
https://bugzilla.gnome.org/show_bug.cgi?id=707897
Modify all visible instances of mutter with mutter-wayland
(libraries, folders, pkgconfig, etc.), so that the wayland
branch can be installed alongside the usual X11 mutter.
https://bugzilla.gnome.org/show_bug.cgi?id=705497