SSL server certificate fingerprint ACL type

This patch add the "server_ssl_cert_fingerprint" acl type to match against
server SSL certificate fingerprint.
The new acl type has the form:
  acl aclname server_ssl_cert_fingerprint [-sha1] fingerprint1 ...

The fingerprint must given in the form:
    XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX
where X are any valid hexadecimal number

Example usage:
acl BrokeServer dst 192.168.1.23
acl GoodCert server_ssl_cert_fingerprint AB:2A:82:AF:46:AE:1F:31:21:74:65:BF:56:47:25:D1:87:51:41:AE
sslproxy_cert_error allow BrokeServer GoodCert
sslproxy_cert_error deny all

This is a Measurement Factory project