Avoid having "@" as the first char in curl_setopt with CURLOPT_POSTFIELDS

Strings, starting with a "@" are treated as file uploads.

See: http://www.php.net/manual/en/function.curl-setopt.php
Sanitize all cURL parameters, not just the message
Adjustments after feedback

* Fixed some comments
* fixed coding style to match rest of the code
* better implementation of the actual fix
Clean up accidentally added whitespace
Merge pull request #11 from apfelbox/master

Avoid having "@" as the first char in curl_setopt with CURLOPT_POSTFIELDS