code: function responsePluginApplyingCallback(cb) {
  	// partly pedantic, partly so the code in the wrapped callback
  	// is shorter; saving plugins here guarantees that plugins added
  	// *after* the request is made, but *before* the response comes
  	// aren't called for this particular request
  	var thisReq = this;
  	var plugins = Plugins.forResponse().asArray();
  	return function (err, res) {
  		plugins.forEach(function (pluginFunc) {
  			pluginFunc.apply(null, [err, res, thisReq]);
  		});
  		cb(err, res);
  	}
  }
docs: private function; called with a Request instance bound to `this`