[krbdev.mit.edu #8060] kinit -C loops chasing realm referrals against MIT KDC

[Greg Hudson via RT]

Commit 3093b92734adfe2deb9ad6bad5a221acc967fd8b (ticket #7856) treats 
PRINCIPAL_UNKNOWN errors as AS realm referrals if the client realm is 
set, to work around the behavior of the Windows Server 2003 KDC.

This change introduced a looping bug against MIT KDCs, which always set 
the client principal and realm in error responses, if an unknown 
principal is requested.  To fix this bug, the client needs to check 
that the client realm is different from the requested realm before 
treating the response as a realm referral.