See libtorrent/TODO for a list of TODO items.

Polling during last phase of shutdown should be very quick, don't use
normal timeout.

Consider basing WindowPeer* on a common base class.

Some kind of indication that a tracker request was tried, but won't be
allowed since the tracker set a min interval.

Make accumulate return the value, no refs please...

>   - seeing the number of seeds / leechers of a torrent on the main
>     screen (and the level of distribution between leechers);

>   - being able to delete not just the torrent file, but the files it
>     created from rtorrent.  Like when you start a torrent, but it is too
>     slow or broken or for various reasons you don't want to download it.