Cannot post files using Request

It's impossible to post files by http using cURL via the Request API.

If you look at the code in the setup_handle method in Requests_Transport_cURL class found in the /Requests/Transport/cURL.php file, you'll see that the POST data is always converted to a string using the PHP http_build_query function. However, according to the PHP manual, the value passed to CURLOPT_POSTFIELDS must be an array if files are passed to this option.

A possible fix could be to simply add the post value to the CURLOPT_POSTFIELDS option as an array if the Content-Type header has been given as multipart/form-data. It would be converted to a query string otherwise. According to the PHP manual, the multipart/form-data Content-Type header will be set if the post value is an array.

In /Requests/Transport/cURL.php, inspect Requests_Transport_cURL::setup_handle and how POST data reaches CURLOPT_POSTFIELDS. Reproduce a multipart/form-data file POST through the Request API and compare it with the non-multipart path. Done means files can be posted successfully while ordinary POST data retains its existing behavior.