The control structure is part of the resolver context.

Use ENABLE_cookies=yes variable to compile functionality.

The cookies layer injects a new query into the plan when a DADCOOKIE
response is detected. After failing the second attempt a TCP fallback is
signalised.

The source address was always put into a subsequent query.

This simplifies the response source identification on the cookie module.

* in the begin() layer, the incoming query is
  exposed as req->qsource.packet, it is invalidated
  after begin() and should not be modified
* the destination address (local interface) is
  also tracked for filtering purposes

during the consume step, the information about
upstream authoritative (address and current rtt)
is exposed in the request structure, just like
information about current query

this change introduces new API for cache backends,
that is a subset of knot_db_api_t from libknot
with several cache-specific operations

major changes are:
* merged 'cachectl' module into 'cache' as it is
  99% default-on and it simplifies things
* not transaction oriented, transactions may be
  reused and cached for higher performance
* scatter/gather API, this is important for
  latency and performance of non-local backends
  like Redis
* faster and reliable cache clearing
* cache-specific operations (prefix scan, ...) in
  the API not hacked in
* simpler code for both backends and caller

* simplified soft-fail per-ns limit to per-query
  limit, each query gets 4 tries at resolving
* instead of locking at single servfailing NS,
  penalise it and run reelection, this may or
  may not try other servers but avoids pathologic
  case when single NS is servfailing while others
  are good but never probed
* added new nsrep update mode (addition)

when raised, a response zone cut will be recovered
even if the response came from cache. this is
normally not needed (and incurs additional cache
lookups), but it may be useful for
inspection

lib: answer finalization was changed