Add a rule to the SecurityGroup object.  Note that this method
        only changes the local version of the object.  No information
        is sent to EC2.

def add_rule(self, ip_protocol, from_port, to_port,
                 src_group_name, src_group_owner_id, cidr_ip):
        """
        Add a rule to the SecurityGroup object.  Note that this method
        only changes the local version of the object.  No information
        is sent to EC2.
        """
        rule = IPPermissions(self)
        rule.ip_protocol = ip_protocol
        rule.from_port = from_port
        rule.to_port = to_port
        self.rules.append(rule)
        rule.add_grant(src_group_name, src_group_owner_id, cidr_ip)