[krbdev.mit.edu #5550] krb5_set_default_tgs_enctypes does not work in Kerberos 1.6

[Tom Yu via RT]

This looks like a duplicate of ticket #4950.  I think what we want to
do is if we get a final ticket via referrals with an enctype not in
the restricted application-requested set, retry with
use_conf_ktypes=old_use_conf_ktypes.