mime类型torrent codeigniter上传文件

I'm trying to upload "torrent" files to server but I get an error "The file type you are attempting to upload is not allowed." i edited the file mime.php:

'btt'   =>  'application/x-bittorrent',

who can help me?

my solution was:

if($_FILES['userfile']['type'] == 'application/x-bittorrent'){
    $config['allowed_types'] = '*';
}