Latest samba4 changes & heimdal breakage

[David Brownlee <abs%absd.org@localhost>]

With the latest samba4 the bundled heimdal no longer builds due to an
updated bundled heimdal.

From the samba 4.16.0 release notes

| Samba has since Samba 4.0 included a snapshot of the Heimdal Kerberos
| implementation.  This snapshot has now been updated and will closely
| match what will be released as Heimdal 8.0 shortly.
|
| This is a major update, previously we used a snapshot of Heimdal from
| 2011, and brings important new Kerberos security features such as
| Kerberos request armoring, known as FAST.  This tunnels ticket
| requests and replies that might be encrypted with a weak password
| inside a wrapper built with a stronger password, say from a machine
| account.

jperkin added support to build with pkgsrc mit-krb5 which neatly
avoids the issue for some systems, but NetBSD ships with heimdal which
complicates matters there.

There is a --with-system-heimdalkrb5 option, but that looks to also
require at least --without-ad-dc to build, (There is a
--with-experimental-mit-ad-dc, but that only works to build with an
external mit-krb5).

Anyone with heimdal-fu free to look at the samba4 build? :)

David