fix dynamic header handling for http (don't add port if using the default)
fix scheme in test + add test for set_msg and dynamic substitution in URL
allow substitutions of URL even if the URL does not start with "%%" (TSUN-279)
doc for xmpp starttls
handle correctly use_proxy in url substitutions (TSUN-279)
enable ssl authentication using client certificate (TSUN-280)
fix documentation (add undocumented features)