[cluttermm_tutorial] actor_events example: Take RefPtr by const ref.

[Murray Cumming <murrayc src gnome org>]

commit 97cff03ba718f7b1393f0caa04e22b9455b01861
Author: Murray Cumming <murrayc murrayc com>
Date:   Mon Mar 28 20:32:14 2016 +0200

    actor_events example: Take RefPtr by const ref.

 examples/actor_events/main.cc |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/examples/actor_events/main.cc b/examples/actor_events/main.cc
index 2a89c4a..589bc84 100644
--- a/examples/actor_events/main.cc
+++ b/examples/actor_events/main.cc
@@ -19,28 +19,28 @@
 #include <iostream>
 
 //Define some functions for the signal handlers to call: 
-bool on_my_button_press(Clutter::ButtonEvent* event, Glib::RefPtr<Clutter::Group> g)
+bool on_my_button_press(Clutter::ButtonEvent* event, const Glib::RefPtr<Clutter::Group>& g)
 {
   g->set_rotation(Clutter::X_AXIS, 330, 0, 0, 0);
   std::cout << "Pressed button at "<< event->x << "/ " << event->y << std::endl;
   return true;
 }
 
-bool on_my_button_release(Clutter::ButtonEvent* event, Glib::RefPtr<Clutter::Group> g)
+bool on_my_button_release(Clutter::ButtonEvent* event, const Glib::RefPtr<Clutter::Group>& g)
 {
   g->set_rotation(Clutter::X_AXIS, 30, 0, 0, 0);
   std::cout << "released button at " << event->x << "/ " << event->y << std::endl;
   return true;
 }
 
-bool on_my_mouse_enter(Clutter::CrossingEvent* event, Glib::RefPtr<Clutter::Group> g)
+bool on_my_mouse_enter(Clutter::CrossingEvent* event, const Glib::RefPtr<Clutter::Group>& g)
 {
   //g->set_scale(1.00, 3.00);
   std::cout << "mouse entered at " << event->x << "/ " << event->y << std::endl;
   return true;
 }
 
-bool on_my_mouse_leave(Clutter::CrossingEvent* event, Glib::RefPtr<Clutter::Group> g)
+bool on_my_mouse_leave(Clutter::CrossingEvent* event, const Glib::RefPtr<Clutter::Group>& g)
 {
   //g->set_scale(3.00, 1.00);