XDamageSubtractAndTrigger behaves exactly like
XDamageSubtract except it receives an optional
fence sync object.  If the value of this object
is not None, it is triggered by X once all the
rendering associated with the damage regions
being subtracted has completed.

Bump version number to 1.3 to match protocol version.

Signed-off-by: James Jones <jajones@nvidia.com>
Reviewed-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Keith Packard <keithp@keithp.com>