md5_file is not supported by PHP < 4.2.0

fscache appears to rely on the md5_file function provided only by php versions 4.2 and greater.

As far as I know, drupal still supports php 4.1.x. The supplemental code to prepend to the fscache.module would be (garnered from the php.net contributed comments for md5_file):

if (!function_exists('md5_file')) {
   function md5_file($file_name)
   {
       if (!file_exists($file_name)) {
           trigger_error('md5_file(): Unable to open file', E_USER_WARNING);
       } else {
           $file_string = implode('', file($file_name));
           return md5($file_string);
       }
   }
}