Password change protocol rework, round 2

[Ken Hornstein]

As previously discussed, I've worked up what I think is a reasonable
implementation of directional address types, based on Sam's outline.  So
far, no problems.

As some people may remember, the whole purpose of this exercise is to get
IPv6 support in the password changing protocol (and clean up everything
associated with the implementation).

While I was doing that, I realized that it would be much simpler and easier
to simply use krb5int_sendto() instead of the code that handles this
explicitly in changepw.c.  But then this brings up another sticky problem ...
retries.

Specifically, what do we do about retries on the server?  We could simply not
have a reply cache (like the KDC by default).  I don't see any dangers in
not having a replay cache on the password changing server at first glance ..
but the idea of it makes me uncomfortable.  Another alternative is to use
a lookaside cache, like the one found in the KDC, but that's a significant
amount of code.  But it's clear to me that we need to improve over the
current situation (one UDP request, no retries).

Comments?  Other ideas?

--Ken