Don't request all info on torrents when summarizing

The number of packets required to do list and similar commands is
significantly reduced. When I did list against a
transmission-daemon with ~500 torrents, the number of packets
dropped from 39924 to 107. This change requires yet unmerged
changes to Transmission::Client; it will work without the
changes, but will not make any difference.

Reference: https://github.com/jhthorsen/transmission-client/pull/5