Bugfix for formatting response to allow multiple Set-Cookie headers

Hi,

we're actually working on a multithreaded, PHP based web server and where looking for a appropriate Fast-CGI client implementation.

While working with your library i faced the problem, that multiple Set-Cookie headers that may returned from applications like Wordpress are ignored, because you add them to an associative array and override each Set-Cookie header with the next one.

I've refactored your formatResponse() method so that it supports multiple headers with the same name (but only one Status header), what should be possible.

Additional we need to change your private methods to be protected because we want to extend your client and work in a multithreaded environment.

Regards
Tim