a bit more cleaning up of m_ses uses in peer_connection

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@10128 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
close files when stopping a torrent

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@10129 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda