Add a kg_encrypt_inplace() utility function to the krb5 GSS mech, and

Add a kg_encrypt_inplace() utility function to the krb5 GSS mech, and
use it where we do in-place encryption of checksums in the non-CFX
seal tokens with raw DES enctypes.  Avoids a harmless but incorrect
in-place memcpy().

ticket: 6770

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@24485 dc483132-0cff-0310-8789-dd5450dbe970