this fixes a bug when storing NODATA without SOA,NS or any other ‘authoritative answer’ hint

since the zone cut is looked up after layers now, it
is pointless to search for minimized names from cache,
since this is the same operation as searching for a zone cut

if the query is satisfied from cache, it doesn’t need a zone cut lookup, so it may be deferred until an outbound query is about the be issued.

since the next CNAME target query was added on top, it replaced
the original ‘current query’, this caused recaching of an answer
if it came from cache (as the query flags have changed)

this prepares cache/txn structures to hold API as well, so we can get
rid of the global api

this fixes a problem when module is unloaded at runtime
and active

memcached is a distributed caching system, it is a good fit
for building resolvers with shared and replicated cache

the module memory not be moved (reallocd), turned array of modules to array of pointers to modules

this fixes a bug where resolution failed, but the finish callbacks thought the answer is noerror

this fixes a regression when a final name has a dependency with a short
TTL in the search path, but has longer TTL itself
in another words - if there's a CDN in the middle and the name doesn't
exist, answer it from the cache without requerying the CDN

This reverts commit 3d1ee641.

This reverts commit ee2cce4d.

previously only queried names were resolved from cache, this meant that if the target name was present in cache but a server on the search path dropped from it, it would refetch it - this is a problem when a loadbalancer with very short TTL was in search path

if the flag is left on, it prevents further caching

the resolution has to start from the root for zonecut resolution, otherwise it might stall resolution if the only good NS drops out of cache and only the bad remain

module api can now store userdata, e.g. owner

the pktcache introduces two cache tags PKT/SEC for
basic/DNSSEC responses and stores negative answers in
the cache