[krbdev.mit.edu #7004] get_creds should restore authdata for non-referral fallback

[Greg Hudson via RT]

r22696 (merged to trunk in r22875) avoids requesting authdata multiple 
times during a referral chain.  But if we fall back from referrals to a 
non-referrals query, we should make that request with authdata, and (if 
we've already received at least one referral before referrals failed) we 
don't.

This bug was introduced in 1.8 and was lovingly preserved in the stepwise 
rewrite of the code for 1.9.  Nico originally discovered the problem 
through code inspection.  It should be very rare in practice.