transition tracker_connections to use shared_ptr instead of intrusive_ptr. optimize udp tracker connection lookups by using unordered map instead of linear search.

git-svn-id: http://svn.code.sf.net/p/libtorrent/code/trunk@10420 a83610d8-ad2a-0410-a6ab-fc0612d85776
first steps towards removing session_impl dependency from tracker connections, to improve their testability

git-svn-id: http://svn.code.sf.net/p/libtorrent/code/trunk@10421 a83610d8-ad2a-0410-a6ab-fc0612d85776
fix bug in setup_transfer (for unit tests). fix verbose logging build. make sure test_pex is reliable

git-svn-id: http://svn.code.sf.net/p/libtorrent/code/trunk@10422 a83610d8-ad2a-0410-a6ab-fc0612d85776