more steps towards isolating peer_connections from the session object. unchoking now happens via the torrent object. hopefully in the future, the session can determine which peers to unchoke without having direct access to them (i.e. with a mutex)

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10319 a83610d8-ad2a-0410-a6ab-fc0612d85776
fix optimistic unchoke stats gauge

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10320 a83610d8-ad2a-0410-a6ab-fc0612d85776
add additional single-thread asserts and separate torrents from the session (in preparation for running them in separate threads/strands)

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10321 a83610d8-ad2a-0410-a6ab-fc0612d85776
post alert on outgoing get_peers

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10322 a83610d8-ad2a-0410-a6ab-fc0612d85776