function onError( child ) {
		return listener;

		/**
		* Callback invoked upon a child process error.
		*
		* @private
		* @param {Error} error - error object
		*/
		function listener( error ) {
			debug( 'Child process error: %s. pid: %d.', error.message, child.pid );
			close( error );
		}
	}
Returns a callback to be invoked upon encountering a child process error.

@private
@param {Object} child - child process
@returns {Callback} callback