Version 3.5.01

Switched all use of hte() to hsc(). hte() is superfluous with UTF-8.
Updated comments about hsc() & hte()
On innHTML = <?php echo addslashes($value) ?>, switched addslashes() to hsc().
System_Setup(): added function validate_units($cssvalue).  Just because.
$_['ext']: changed from just 'ext' to  '.ext';
New: $_['folders_first_info']
Added hsc() where needed in a few places.
New: function Send_data_to_js().  Split out from Index_Page().
Get_DIRECTORY_DATA(): check if file_exists() in case of encoding error.
Index_Page_scripts(): changed some js CONSTANTS & flags for sort_DIRECTORY().
sort_DIRECTORY(): Changed logic. A little more verbose, but seems clearer.
In prep for an upcoming bug fix:
  added $ENC_OS, $ENC_UA, and $CLIENT_OS
  Also, tagged several places (with //##### ) where file system calls are made.
  The $filename strings used in the calls may need to be encoded with something
  other than UTF-8, depending on the underlying OS's filesystem.
    (such as NTFS, which uses UTF-16)