add additional single-thread asserts and separate torrents from the session (in preparation for running them in separate threads/strands)

git-svn-id: http://libtorrent.googlecode.com/svn@10321 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
post alert on outgoing get_peers

git-svn-id: http://libtorrent.googlecode.com/svn@10322 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda