function next( child ) {
		var numPending;
		idx += 1;
		if ( idx >= files.length ) {
			numPending = objectKeys( pending ).length;
			if ( numPending > 0 ) {
				debug( '%d scripts are pending.', numPending );
				return;
			}
			debug( 'All scripts have finished.' );
			return close();
		}
		debug( 'Instructing child process to run script: %s. pid: %d.', files[ idx ], child.pid );
		child.send( files[ idx ] );
		pending[ files[ idx ] ] = true;

		debug( '%d of %d scripts have been processed.', idx, files.length );
	}
Instructs a child process to run the next script.

@private
@param {Object} child - child process
@returns {void}