* automatic connection loss recovery
* dhtrunner: asynchronous DNS lookup for bootstrap
* handle values up to 64k
* better support for large values on macOS
* dht: add callback to pingNode
* fix compilation with recent clang versions

search: detect connectivity changes

The number of bad nodes is limited in order to help determine presence of
connectivity changes. See https://github.com/savoirfairelinux/opendht/issues/137
for details.

According to the tables, 25 is a good average value for big networks. If the
network is small, normal search expiration process will handle the situation.

dhtrunner: recover from network changes

network: transmit large values in multiple packets

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

This is to prevent any thread relying on network_engine's callback to block
forever just like the Dht::sendPing's callback.

Using a list of bootstrap nodes, we recover from network loss by pinging those
nodes continuously until connected.
Written with Simon Désaulniers.

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.