display: don't report extended barrier support on wayland

Even if the xserver does them, they're useless because it doesn't
get the pointer events.
This is a lame workaround for not having real barriers in wayland,
but it fixes the hot corner and message tray (because it triggers
the old xserver path)
MonitorManager: add a KMS backend

Using the new Cogl API to actually modeset (because we can't
use the DRM API directly without controlling buffer swap), we
can finally have a KMS monitor backend, which means full display
configuration when running on bare metal.

https://bugzilla.gnome.org/show_bug.cgi?id=706308
MetaWaylandSeat: don't use use events to count pressed buttons

Use the modifier mask instead, as events can get lost if there
is a clutter grab or if some other actor is capturing events.

https://bugzilla.gnome.org/show_bug.cgi?id=706124
wayland: implement global and window keybindings

Synthetize XInput events from ClutterEvents in MetaWaylandKeyboard,
and pass them to the keybindings infrastructure for early handling,
so that we can activate them even if the currently focused window
is not an X11 one (or if there is no focused window, or we're
modal)

https://bugzilla.gnome.org/show_bug.cgi?id=706963
wayland: constraint the pointer onto visible monitors when running on evdev

Use the new Clutter hook to make sure the pointer never enters
the dead area caused by the different monitor sizes.

You don't realize how much X is doing for you until you lose it...

https://bugzilla.gnome.org/show_bug.cgi?id=706655
[NOT FOR REVIEW] Add the ability to attach a debugger at init
Set DISPLAY and WAYLAND_DISPLAY for dbus activated services and for autostarted apps

Call the appropriate method on gnome-session so that autostarted
and bus activated apps see the X server and wayland socket.

https://bugzilla.gnome.org/show_bug.cgi?id=706421
Stop messing with process groups

We can be launched by gnome-session now, which implies gdb must be
attached from outside, and the Ctrl-C problem is gone.

https://bugzilla.gnome.org/show_bug.cgi?id=706421
wayland: don't require Clutter backend variables to be set from outside

When running under mutter-launch, we can assume we're running on
bare metal, and set the clutter backend appropriately.

https://bugzilla.gnome.org/show_bug.cgi?id=706421
wayland: die when gnome-session asks us to

At logout, we want to die when gnome-session tells us. Previously,
we were relying on the X server going down (killed by GDM at the
end of the session), but we can't use that in wayland.

https://bugzilla.gnome.org/show_bug.cgi?id=706421