fix another boost.chrono issue

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10113 a83610d8-ad2a-0410-a6ab-fc0612d85776
fix todo comment

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10114 a83610d8-ad2a-0410-a6ab-fc0612d85776
separate stats counters from session_interface (this was the main use of m_ses in peer connections)

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10115 a83610d8-ad2a-0410-a6ab-fc0612d85776
removed unused session_impl member, m_next_disk_peer

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@10116 a83610d8-ad2a-0410-a6ab-fc0612d85776