watchdog cleanup and loop clock object

supervisor/session/plc.lua

@@ -403,7 +403,7 @@ plc.new_session = function (id, for_reactor, in_queue, out_queue)
 
     -- check if a timer matches this session's watchdog
     local check_wd = function (timer)
-        return timer == self.plc_conn_watchdog.get_timer()
+        return self.plc_conn_watchdog.is_timer(timer)
     end
 
     -- close the connection