Changed code to avoid gcc warning when -W and -Wall are used together.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403016

examples/bayes_net_gui_ex.cpp

@@ -959,7 +959,7 @@ on_evidence_toggled (
 
 // This event is called when the user causes no node to be selected 
 void main_window::
-on_node_deselected ( unsigned long n )
+on_node_deselected ( unsigned long  )
 {
     no_node_selected();
 }