Regularize the handling of KRB5_AUTH_CONTEXT_RET_SEQUENCE in
krb5_mk_safe, krb5_mk_priv, and krb5_mk_ncred, using krb5_mk_safe as
a baseline. RET_SEQUENCE now implies DO_SEQUENCE for all three
functions, the sequence number is always incremented if it is used,
and outdata->seq is always set if RET_SEQUENCE is passed.
Note that in the corresponding rd_ functions, RET_SEQUENCE and
DO_SEQUENCE are independent flags, which is not consistent with the
above. This compromise is intended to preserve compatibility with
any working code which might exist using the RET_SEQUENCE flag.
Commit By: ghudson