Fix DND keyboard control with XI2

We are using XI2 to grab the key events, but we did not do the
necessary extra work to make GDK deliver root window events to us.

https://bugzilla.gnome.org/show_bug.cgi?id=681006

gtk/gtkdnd.c

@@ -411,6 +411,18 @@ root_key_filter (GdkXEvent *xevent,
   if ((ev->type == KeyPress || ev->type == KeyRelease) &&
       ev->xkey.root == ev->xkey.window)
     ev->xkey.window = (Window)data;
+  else if (ev->type == GenericEvent)
+    {
+      XGenericEventCookie *cookie;
+      XIDeviceEvent *dev;
+
+      cookie = &ev->xcookie;
+      dev = (XIDeviceEvent *) cookie->data;
+
+      if (dev->evtype == XI_KeyPress ||
+          dev->evtype == XI_KeyRelease)
+        dev->event = (Window)data;
+    }
 
   return GDK_FILTER_CONTINUE;
 }