this is useful when you need to issue several subrequests before
continuing with the current query, resuming is not supported yet, so it
will requery after the subrequests complete

current processed query is always in `request->current_query`

thanks to johan ihren

when no validation is attempted, trust level is 'bad'
when validation attempted but insecure, trust level is 'insecure'
otherwise 'secure'

minimised nodata/nxdomain can now be cached if it is
authoritative. also pkt/sec cache are now shared using
the ‘rank’ field to replace insecure version with secure
if needed

this is a workaround for missing DEFER operation, as the
validator module can only detect trust chain breakage
(caused by answering from different authority) after the
iterator writes answer. this causes duplicated answer on
uncached queries

this doesn’t fix record duplication in answer when not answered from cache

missing boundary checking and bad offset calculation

todo:
the code presumes little endian, didn’t get to  fix that

if the query has RD=0 or is ANY, only cache is probed
for ANY, only A/AAAA/MX is checked and no query is
forwarded to the authoritatives

i.e. if the user doesn't set the cache, it will be applied later
if he sets it, it will stay

this is going to be needed for issuing multiple timed queries + fast
retry

effectively enables/disables usage of given IP protocol
for subrequests (the server can still listen on these)

if the answer is flagged as insecure, it means that the resolver tried
to validate it, but couldn't (e.g. trust chain doesn't exist)

- can query cache for records
- can remove only domain or subtree from cache
- can remove data in packet cache or other prefixes
- cache clear also reset NS reputation tracking

the key is now stored in a format friendly to prefix search, the values
also contain one more 16bit field to store rank of the data (to be
utilised later)