Modernize KRB-PRIV/KRB-SAFE/KRB-CRED functions

Modernize KRB-PRIV/KRB-SAFE/KRB-CRED functions

In krb5_mk_safe(), krb5_mk_priv(), krb5_mk_ncred(), krb5_rd_safe(),
and krb5_rd_priv(), modify naming, formatting, and memory management
to meet current standards.  Add k5_privsafe helpers to generate replay
data and addresses and to store replay records.  For krb5_mk_ncred(),
expand the contract of the encoding function to be similar to the
other two krb5_mk functions, and use pointer aliases to reduce the
number of copies required.