Enable XI2 by default

gdk_enable_multidevice() has been replaced with gdk_disable_multidevice(),
so applications may call that function if they want to go back at the
previous behavior.

There would be usually little reasons to call that function, unless the
application is doing X calls itself that count on old fashioned core
devices.

gdk/x11/gdkdevicemanager-x11.c

@@ -48,7 +48,7 @@ _gdk_device_manager_new (GdkDisplay *display)
           major = 2;
           minor = 0;
 
-          if (_gdk_enable_multidevice &&
+          if (!_gdk_disable_multidevice &&
               XIQueryVersion (xdisplay, &major, &minor) != BadRequest)
             {
               GdkDeviceManagerXI2 *device_manager_xi2;