Instead of relying on gnome-settings-daemon to set up _XROOTPMAP_ID
properly, do rendering in process and stuff the background into a normal
texture.
This will allow to do more fancy transitions in the future, using
Clutter to drive them.
https://bugzilla.gnome.org/show_bug.cgi?id=682427
XInput 2.3 adds support for "barrier events", which let us know when
a pointer barrier has been hit, and when the pointer has stopped
hitting the barrier, and lets us "release" the barrier, temporarily
letting the pointer pass through the barrier. These features can be
combined to allow for certain pointer gestures, such as "pushing"
against the bottom of the screen, or stopping the pointer on monitor
edges while dragging slowly for increased edge precision.
This commit should allow graceful fallback if servers with
XInput 2.3 aren't supported.
https://bugzilla.gnome.org/show_bug.cgi?id=677215
