Solve private download problem

Hi

If you add:

function filemime_file_download($filename) {
  $fullpath = file_create_path($filename);
  if (file_exists($fullpath)) {
    $filesize = filesize($fullpath);
    return array(
      'Content-Type: '. mime_header_encode(file_get_mimetype($filename)),
      'Content-Length: '. $filesize,
    );
  }
  return -1;
}

to the filemime.module it solves the problem that user have when downloading files with
private download method (ie Drupal always returns text/plain as mime type)!

This will make this module (even without overrides) even much more usefull!