When z.Tree.Prev returns zero we should break out of this loop, not
use elem as if nothing has happened.
Can be triggered by sending edns0 to unsigned zone.
DS is peculiar and needs some special cases to do the right things.
For a direct query return the DS, but if we're hitting below the
delegation return the NS+DS in a delegation response.
Don't put NS records in the answer section; if we see it is delegated
we should put the records in the AUTHORITY section.
This removes a special case, which is good.
* Rename middleware to plugin
first pass; mostly used 'sed', few spots where I manually changed
text.
This still builds a coredns binary.
* fmt error
* Rename AddMiddleware to AddPlugin
* Readd AddMiddleware to remain backwards compat
