libuv doesn't do connected UDP sockets, so we can't get ICMP unreachable
otherwise

previously if NS had no A/AAAA records, they we’re looked up in subrequests, after that a new NS was reelected (possibly preferring another unknown), now it stays true to the NS of choice and changes only if it is unuseable

this LRU-like cache tracks lame nameservers, unresolvable
nameservers (to not waste resources in trying to resolve them),
and possibly other features (extension support, …)

when a NS is in the TIMEOUT, it can’t be autoselected by default but only probed after a successful dice roll - however in some scenarios we’d like to probe timeouting servers more thoroughly 

simplified bee foraging strategy, by default each query goes to the most rewarding NS
however with a chance proportional to the NS RTT, a server may be probed even if it isn’t the most rewarding

score has now meaning of ‘RTT’, maximum RTT is 10s
which is also the penalty for timeout
unknown servers are favorized as 10ms servers to
encourage resolver to try them out, if they contain
unknown glue they are most favourable

nameservers with addresses are preferred, the rest
has same weight

no blacklisting, penalization or rtt scoring yet