(qt) when changing the session's download dir, call session-get to update the freespace value

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@13889 f4695dd4-2c0a-0410-b89c-da849a56a58e
(libT) rename internal struct 'tr_torrent_peers' as 'tr_swarm'

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@13890 f4695dd4-2c0a-0410-b89c-da849a56a58e