http file transfer may fail unnecessarily
The http file transfer plugin (multifile_curl_plugin) relies on the Content-Length header being present GET request. If Content-Length is not present, then the file transfer will fail after 30 seconds even if the transfer is making good progress. Because Content-Length header is not required, it may be omitted in certain circumstances, and thus our plugin should not rely upon it in order to determine if the transfer is making progress.
Code review: looks good to me