fix test_checking

git-svn-id: http://libtorrent.googlecode.com/svn@10419 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
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://libtorrent.googlecode.com/svn@10420 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda