fix ip_voter to detect changing IPs

git-svn-id: http://libtorrent.googlecode.com/svn@9758 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
merged changes from trunk

git-svn-id: http://libtorrent.googlecode.com/svn@9759 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda