code: function(C, action, thisp) {
  		if (C && C.$superclass) {
  			action = action || gui.Combo.identity;
  			return action.call(thisp, C.$superclass);
  		}
  		return null;
  	}
docs: Return superclass. If action is provided, return the result
  of executing the action with the superclass as argument.
  @param {function} C constructor
  @param @optional {function} action
  @param @optional {object} thisp
  @returns {gui.Class|object}