Deduplicate on recent IPs

[CorralPeltzer]

Some trackers, like udp://tracker.torrent.eu.org:451, seem to use DNS round robin. They also resolve to subdomains like www.torrent.eu.org.

This makes it possible that at some point, while tracker.torrent.eu.org resolves to IPv4 A and IPv6 B, www.torrent.eu.org is submitted and resolved to IPv4 X and IPv6 Y, being accepted as a new tracker (different domain and disjoint sets of IPs). To avoid this, newTrackon should keep a record of the last N IPs resolved by a tracker and deduplicate trackers also based on these IPs.