Implement client_key and client_cert support in curl_httpclient.
Implement client_key and client_cert support in curl_httpclient.

+ will push the changes upstream when we've exercised them more.

ultilix/catawampus,shineyear/catawampus,pombredanne/catawampus,ankurjimmy/catawampus,pombredanne/catawampus,ultilix/catawampus,shineyear/catawampus,ankurjimmy/catawampus