Implement additional-from-{glue,auth} [ yes | no ] ;
with yes being the default.  These control searching in the cache and
other zones we are authorative for.  This is mostly for gdib, but
may be useful elsewhere.

The config changes are renaming from glue-from-* to additional-from-*,
since this also prevents DNAME, CNAME, NS, MX, etc. additional data
from being followed.