Adjust to change of Broadcast.cancel method.

src/altk/comm/engine/CommEngine.java

@@ -344,7 +344,7 @@ public abstract class CommEngine extends HttpServlet
             out.format("Broadcast %s does not exist", broadcastId);
             return;
         }
-        broadcast.cancel();
+        broadcast.cancel(out);
     }
     
     protected void pauseBroadcast(HttpServletRequest request, PrintWriter out)