[XInput] Get XInput working again.

Check for distros shipping out of sync header vs libXi,
call in g_type_init() in test-devices, fix ifdef so
XInput events get correctly selected.

tests/interactive/test-devices.c

@@ -33,6 +33,8 @@ test_devices_main (int argc, char **argv)
   TestDevicesApp *app = NULL;
   ClutterColor stage_color = { 0x61, 0x64, 0x8c, 0xff };
 
+  g_type_init();
+
   clutter_x11_enable_xinput ();
   clutter_init (&argc, &argv);