Thanks for the long review.

I think I've addressed all your comments except the ones noted below:

>   o What benefit do the non-NULL checks in commit 3eb5aad6e9 bring?  I
>     was unable to figure out a code path which would cause these checks
>     to evaluate to false.  Also, there are other instances of
>     ns_server_detach() calls without a similar non-NULL check (e.g. in
>     clientmgr_destroy() in lib/ns/client.c).

I think I prefer to keep them, at least for now, as it just seems like a
good pattern to check before detaching.  I know of no reason to expect them
to be NULL, but it helps to future-proof the code.

>   o Commit c336ed47ba moves the isself() callback back into
>     bin/named/zoneconf.c.  However, I was unable to quickly figure out
>     why that is needed or desired.

Sorry, I can't recall now. It may just have seemed aesthetically
righteous. Perhaps I realized my earlier move of the code was
unnecessary and so I figured it shouldn't be done.

>   o Commit cfb4fc12f8 "incidentally fixes a potential problem with
>     dns_aclenv_destroy()".  Could you please explain what that potential
>     problem is?  If you discovered a code path which causes erroneuous
>     behavior, can it be reproduced in a test?

I don't remember the reason for this now either, sorry.

>   o A lot of function prototypes in lib/ns/include/ns/ are not
>     commented:

You're right, that needs doing. I'll get to it later, though.

Can you go over commit ad416a5f90 and confirm that it addresses the
concerns you raised?