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

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

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code@10322 a83610d8-ad2a-0410-a6ab-fc0612d85776
added auto-sequential feature

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code@10323 a83610d8-ad2a-0410-a6ab-fc0612d85776