ws/i965: add load-time driver registration

Otherwise xlib state-tracker doesn't know about us.

src/gallium/winsys/drm/i965/xlib/xlib_i965.c

@@ -360,6 +360,13 @@ struct xm_driver xlib_i965_driver =
 };
 
 
+/* Register this driver at library load: 
+ */
+static void _init( void ) __attribute__((constructor));
+static void _init( void )
+{
+   xmesa_set_driver( &xlib_i965_driver );
+}