Starting from Transmission 2.80 (rpc-version-semver 5.1.0, rpc-version:
15) 'torrent-add' could return 'torrent-duplicated' from torrent-add if
the torrent already exists. Replace 'TorrentAdded' with
'TorrentAddedOrDuplicate'.
Changes client setup in every example so that it checks whether both the
TUSER and TPASS environment variables are set and, if not, assumes no
basic auth.