Support for ChallengeResponseAuthentication in Match section

[Alexander Afonyashin]

Hi,

I'm using 2-factor authentication (pubkey+googe_authenticator) and
have an issue with rsync. It's configured to use pubkey to
authenticate to server so when google_authentication is bypassed by
not creating .google_authenticator file for particular user (thanks to
nullok option in PAM) it still sends to stderr "Authenticated with
partial success." message although it succeeded.

So idea is simple: disable 2-factor authentication for particular user/network.

Regards,
Alexander