quick hack to get rate-faster/slower to react in qt4 interface, there's

something fishy in here because seems that inputmanager doesn't get
variable callbacks regarding input-rate from /src/input/input.c. 
Slider worked because we set ourself that rate-variable, or atleast it seems
so.

modules/gui/qt4/input_manager.cpp

@@ -138,6 +138,8 @@ void InputManager::addCallbacks()
     var_AddCallback( p_input, "video-es", ChangeVideo, this );
     /* src/input/input.c:1765 */
     var_AddCallback( p_input, "rate", ItemRateChanged, this );
+    var_AddCallback( p_input, "rate-faster", ItemRateChanged, this );
+    var_AddCallback( p_input, "rate-slower", ItemRateChanged, this );
     /* src/input/input.c:2003 */
     var_AddCallback( p_input, "title", ItemTitleChanged, this );
     /* src/input/input.c:734 for timers update*/
@@ -151,6 +153,8 @@ void InputManager::delCallbacks()
     var_DelCallback( p_input, "video-es", ChangeVideo, this );
     var_DelCallback( p_input, "state", ItemStateChanged, this );
     var_DelCallback( p_input, "rate", ItemRateChanged, this );
+    var_DelCallback( p_input, "rate-faster", ItemRateChanged, this );
+    var_DelCallback( p_input, "rate-slower", ItemRateChanged, this );
     var_DelCallback( p_input, "title", ItemTitleChanged, this );
     var_DelCallback( p_input, "intf-change", InterfaceChanged, this );
 }