/etc/rc.d/named minor problems.

I founs some minor problems with /etc/rc.d/named in 5.3RC1 and work a 
patch on this.  I think this must be vaild for HEAD.

- add a ${named_chroot_mtree}, so /etc/mtree/BIND.chroot.dist don't need 
rewrite to alter chroot layout.

- supress /etc/named link code.  This don't seems really needed here.
Also, detect problems with this.  IMHO, this must be carefully take in 
installworld/mergemaster.

- move devfs code to named_precmd.  This seems to be needed in any case, 
not only in chroot autoupdate.

patch attached.

--
  josemi