[NOT FOR REVIEW] Add the ability to attach a debugger at init
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: sync the keymap from X to wayland

When X clients change the keyboard map, the also update a property
on the root window. We can notice that and rebuild our data structures
with the new values, as well as inform the wayland clients.

This is a terrible hack, and it's not how we want to implement things
in 3.12, but it's enough to have the same keyboard layout in the
shell, in X clients and in wayland clients in 3.10, until we decide
on the fate of the keyboard g-s-d plugin.

https://bugzilla.gnome.org/show_bug.cgi?id=707446
wayland: use the timestamps from events

Clutter has learned to use monotonic times for the events, and
so does X (at least Xwayland, which is an implementation we know
and we can rely upon), so the values are directly comparable.

https://bugzilla.gnome.org/show_bug.cgi?id=707466
display: shortcut get_time_roundtrip() when running as a wayland compositor

In wayland, we can make some assumptions about the behavior and
configuration of the X server (which is Xwayland), including on
the time it uses, and that way avoiding a roundtrip (potentially deadly, if
by chance the X server is also blocking on us or needs us to flush
the wayland socket buffer).
Note that we bypass get_current_time() entirely, as it is assumed
the function is called always to translated CurrentTime into a real
value.

https://bugzilla.gnome.org/show_bug.cgi?id=707466
wayland: add support for pointer barriers

Use the clutter pointer constrain callback and a lot of copypasted
code from Xorg to implement reactive pointer barriers and pointer
barrier events.

https://bugzilla.gnome.org/show_bug.cgi?id=706655