Support for Windows Server 2003 referrals

[Nate Rosenblum]

All--

I've submitted a pull request that allows referrals to work in Windows
Server 2003 forests. The issue is described in the patch, but in short
Server 2k3 uses the wrong error type (PRINCIPAL_UNKNOWN) to indicate a
referral. I speculate that this continues to be the case in later
service releases for backwards compatibility, 2k3 predating the
referrals draft, but don't really have any context.  Let me know if
there are any questions.

https://github.com/krb5/krb5/pull/39

Best,

--nate