If sorting is enabled directories and files will be sorted independently with
directories appearing before files in the resultant array that is returned.
Any parameter returned by stat is a valid sort parameter for this function.
Filename comparisons are case insensitive.
Examples:
$sftp->setListOrder('filename', SORT_ASC);
$sftp->setListOrder('size', SORT_DESC, 'filename', SORT_ASC);
$sftp->setListOrder(true);
Separates directories from files but doesn't do any sorting beyond that
$sftp->setListOrder();
Don't do any sort of sorting