Added support for `CurlFile` for multipart requests to prevent deprecated warnings in PHP 5.5.

Example call:

    $client->request('POST', 'https://api.twitter.com/1.1/statuses/update_with_media.json', array(
      'status' => ‘Posting a photo’,
      'media[]' => new CurlFile(‘my-file.jpg’),
    ), true, true);