st-scroll-view: Throw away emulated pointer events

These are sent by the X server and have large deltas. They really
should be filtered out by Clutter (or the X server) somehow, but we
don't have the means to do that yet.

https://bugzilla.gnome.org/show_bug.cgi?id=687573

src/st/st-scroll-view.c

@@ -731,6 +731,9 @@ st_scroll_view_scroll_event (ClutterActor       *self,
   if (!priv->mouse_scroll)
     return FALSE;
 
+  /* throw away this garbage event. we want smooth scrolling. */
+  if (clutter_event_is_pointer_emulated ((ClutterEvent *) event))
+    return TRUE;
 
   switch (event->direction)
     {