function onMessage( child ) {
		return listener;

		/**
		* Callback invoked upon receiving a message from a child process.
		*
		* @private
		* @param {string} filepath - script filepath
		*/
		function listener( filepath ) {
			debug( 'Child process message: %s. pid: %d.', filepath, child.pid );

			// Remove the script from the listing of pending scripts:
			delete pending[ filepath ];

			// Indicate that the child process is ready for its next task:
			next( child );
		}
	}
Returns a callback to be invoked upon receiving a message from a child process.

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