Messages transitioning multiple times in the same Authserv-ID produce result of fail

[abeverley]

If a message is received and verified in the same Authserv-ID domain, if it then transitions to other systems within the same domain, the ARC result becomes fail.

E.g.

1. An email is received from an external source by server1.example.com.
2. The email is verified and then signed using the Authserv-ID example.com and then sent onto server2.example.com.
3. That second server then also tries to verify and sign using example.com.
4. OpenARC will always produce an ARC signature with the result fail.

This is because commit f6b57dc results in multiple authentication-results in the same Authserv-ID always producing a fail.