Importing SslBump feature from Squid3 ssl-bump branch:

Importing SslBump feature from Squid3 ssl-bump branch:

        SslBump needs access to SSL-related options when responding to
        CONNECT requests. We could add a new squid.conf option to
        accept those options, but I decided to add SSL-related options
        to http_port, where CONNECT requests will arrive. This design
        avoids the necessity to map SSL options to an HTTP port or to a
        CONNECT request when a global default would not do.

        Adding SSL options to http_port makes http_port_list and
        https_port_list almost identical. I moved stuff around to
        reduce duplication between the two classes, moving related
        code to ProtoPort.{cc,h} in the process. More work is needed
        to remove the distinction completely or, at least, remove the
        https_port::http hack.

        Added support for ssl_error ACL (ACLSslError*).