gtktreeview: don't handle extra mouse buttons

Don't handle mouse button events greater than 5 so
they can bubble up to be used by the application.

This was causing nautilus list view to not go forward
and backwards when pressing the extra mouse buttons
designated for that.

Fixes bug 673441

Signed-off-by: Nelson Benitez Leon <nbenitezl@gmail.com>

gtk/gtktreeview.c

@@ -2876,6 +2876,10 @@ gtk_tree_view_button_press (GtkWidget      *widget,
 			"horizontal-separator", &horizontal_separator,
 			NULL);
 
+  /* Don't handle extra mouse buttons events, let them bubble up */
+  if (event->button > 5)
+    return FALSE;
+ 
   /* Because grab_focus can cause reentrancy, we delay grab_focus until after
    * we're done handling the button press.
    */