Bugfix to avoid breaking XML in case of special characters

In case xml contains special characters like the ampersand, the resulting xml in transport is broken. Urlencoding seems to help, see:

http://www.php.net/manual/en/function.curl-setopt-array.php

"As with curl_setopt(), passing an array to CURLOPT_POST will encode the data as multipart/form-data, while passing a URL-encoded string will encode the data as application/x-www-form-urlencoded."

Dunno if this is the optimal solution but seemed to help in my case.