Assortment of unimportant changes that I created during trying to understand how the whole resolution process works. Best read each commit separately.

if the score is known (and not glued), the retry
rate is <avg(rtt), 250ms>

if the NS score is unknown or worse than 250ms,
it is always retried at this rate

all other servers in the list use default rate

maintainer may wish to choose neutral or even
more favoured server selection of IPv6 servers.

-DFAVOUR_IPV6=0 makes neutral server selection
-DFAVOUR_IPV6=40 gives IPv6 40ms better chance

RTT tracking for all targets is also supported,
but no loadbalancing is done based on that yet

Consequently, there's no use for worker_reserve in the header.

Also break overlong lines.

The last hunk: we'd report worker failure even if we didn't
attempt to start it due to previous failures.

We called kr_crypto_init() just before forking and then _reinit() in
all children, but we never did any cryptography in-between - better
initialize after forking.

Note: the function is KR_EXPORT.  It might not be useful anymore, but
its removal would require bumping libkres soname.

Reported: https://gitlab.labs.nic.cz/knot/resolver/issues/92

timeouts over TCP when <n> first nameservers timeout over UDP as
previously the TCP would connect again to the first and only the
first nameserver in task->addrlist.

This would need to be ultimately fixed in TCP Fast Retransmit.

when doing fast retransmit, each address may be
contacted 1-N times, but previously only cumulative
RTT was tracked for the NS that sent the answer.

now the approximate query start time is subtracted
from cumulative RTT to give an idea how long it
took since the query was actually sent, and all
the NSs that didn't respond within their retransmit
windows are penalised too

bcf3f4b5 made query_finalize() to be called on
each outbound query before sending, so each
retransmitted query got different 0x20 case
and the only responses from the latest contacted
NS matched.

reverted back the old behaviour where query case
is randomised when an outbound query is generated,
not before sending

REFUSED response no longer causes retry in
iterator when operating in stub mode

example:

> daf.add 'forward 127.0.0.1@5353'

The missing entry caused some entries to be dear and written to wrong
positions.

DNS Cookies

Second merge request introducing DNS cookies.

See merge request !38