[PATCH] update port protocol parameter

This patch updates the *_port directives protocol= parameter to accept
to use AnyP::ProtocolVersion internal storage instead of opaque string text.

This both limits the possible parameter values to one of HTTP, HTTP/1.1,
HTTPS, or HTTPS/1.1 and ensures that URLs generated from that protocol
parameter value are http:// and https:// URL.

Amos