Support for `CurlFile` for multipart requests to prevent deprecated warnings in PHP 5.5

Example call:

```php
$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);
```