add unit test to make sure the next tier is tried in the tracker list when the one ahead of it fails
add unit test to make sure the next tier is tried in the tracker list when the one ahead of it fails

aindigo/rasterbar_libtorrent,aindigo/rasterbar_libtorrent,aindigo/rasterbar_libtorrent,aindigo/rasterbar_libtorrent,aindigo/rasterbar_libtorrent,aindigo/rasterbar_libtorrent