Adding password-expiration LAST_REQ message.

[Ken Hornstein]

We have an old change to the MIT KDC that returns a password expiration
time in the last-req field of the ticket.  It also includes a KDC
configuration entry to specify a time limit for sending the message
(like if the password expiration is occuring within a week).  The
client support for this already exists in MIT Kerberos.  Would this
change (cleaned up and documented) be welcome to be submitted?

--Ken