issue with /etc/rc.d/mountd script

Greetings all.

I saw something the other day on a machine running 10/stable
(but the same code exists in -current), when it was rebooting.

The machine acts as a NFS fileserver (to support diskless booting
of a few test machines).  It only has ZFS filesystems, and only
has filesystems that are exported via ZFS properties.

So, it has /etc/zfs/exports, but no /etc/exports.

When mountd is started up, it emits a error, because the
required_files is set to /etc/exports.

I think the correct thing is to either remove the required_files
setting, or build it from /etc/exports and/or /etc/zfs/exports
and only fail if neither of those files exists.

(Yes, I could just create an empty /etc/exports file, but that's
kinda lame.)

-Kurt