code: public SpoutDeclarer setSpout(String id, IControlSpout spout) {
          return setSpout(id, spout, null);
      }
docs: Define a new bolt in this topology. This defines a control spout, which is a simpler to use but more restricted kind of bolt. Control spouts are intended for
  making sending control message more simply
  
  @param id the id of this component.
  @param spout the control spout