add transfer capability and small ways to test it

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@1290 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/include/switch_module_interfaces.h

@@ -60,6 +60,8 @@ struct switch_state_handler_table {
 	switch_state_handler on_loopback;
 	/*! executed when the state changes to transmit*/
 	switch_state_handler on_transmit;
+	/*! executed when the state changes to hold*/
+	switch_state_handler on_hold;
 };
 
 /*! \brief Node in which to store custom outgoing channel callback hooks */