dht: bug fixes, timing computation enhancements

'find_node' requests don't ask for values. Then, the idea of a Query makes less
sense, but since we still need those to map status to network engine requests,
we introduce dummy queries which with the field Query::none. Those queries will
then only serve as key to network engine's requests.

When no listen request have been sent yet, getListenTime should tell it's okay
to send pending listen request.

Replace with -DCMAKE_BUILD_TYPE=Debug

dht: use a map for storage

introduce SockAddr to store IP addresses

[dht] concurrent queries

More code encapsulated in objects method is better for keeping consistent
behavior.

The code preceding this would just not take multiple concurrent queries for a
same search into account. This is a bug fix for a bad behavior since the
queries.

The criteria has been rewritten (again) exploiting the idea behind the parameter
'update' to take into account the case where we have new distinct requests to
send, then bypass some checks.

Simon Désaulniers authored 8 years ago and Adrien Béraud committed 8 years ago

The 'put' operation will now first check if nodes already store the value we
have to announce. If so, we don't announce it to that node.

dht: Dht::insertNode has to really insert

crypto: drop support for GnuTLS < 3.3