Getting the _session_id from SWFUpload

It appears that Ruby's CGI::Session class will not use the _session_id in the query string when the Request is a POST.

Normally, a POST-type request occurs when a form is submitted to the server (e.g. a Rails application). In this scenario, there is an easy workaround since we can send the _session_id as a hidden field.

With Flash 8, however, there is no way to add a 'hidden field' to the multi-part form data, thus Rails will fail to recognize the _session_id in the query string portion of our request.