I've modified our software (racoon2's kinkd) to use krb5_c_prf()
instead of our own PRF implementations, and noticed that krb5_c_prf()
supports only AES etypes.  Why not for other etypes?

At least des3-cbc-sha1-kd is easy with the attached patch.
It is interoperating with ours well.

# If there are any interests in des etypes, I'll send them as well.