r9648: this fixes the krb5 based login with the pac. The key to this whole saga was

r9648: this fixes the krb5 based login with the pac. The key to this whole saga was
that the logon_time field in the pac must match the authtime field in the ticket we
gave the client in the AS-REP (and thus also the authtime field in the ticket we get
back in the TGS-REQ).

Many thanks to Andrew Bartlett for his patience in showing me the
basic ropes of all this code! This was a joint effort.