* 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.