* lock passing between add_peer_to_torrent and return_peers_for_torrent is now avoided by providing a more general add_peer_to_torrent_and_return_peers function that can be used with NULL parameters to not return any peers (in sync case)
* in order to keep a fast overview how many torrents opentracker maintains, every mutex_bucket_unlock operation expects an additional integer parameter that tells ot_mutex.c how many torrents have been added or removed. A function mutex_get_torrent_count has been introduced.
1. stats for added and removed torrents
2. stats for start and stopped events from peers
this should help to detect DoS attacks and is useful for
profiling