[krbdev.mit.edu #1621] aes checksum types not implemented

[Ken Raeburn via RT]

Okay, with the fencepost error fixed in the heimdal-20030623 snapshot,
and the AES enctype added to set_keys.c:make_keys, I was able to
create a database, and add a user principal.  I could then use the MIT
client programs to get a TGT and then get a service ticket for the
same test principal, all using AES keys.  So, it looks like our
support for the new checksum types -- at least, the flavor using the
256-bit AES key -- is working compatibly with Heimdal.

I'll mark it for pullup to the 1.3 branch, and file a separate bug
about our not using it by default when creating various message types.

Ken