In legacy/trac#17840 in 0.2.8.1-alpha, we sometimes fail to fall back to directories with addresses in non-preferred IP families: * we didn't identify relays that we could fall back to correctly; * we incorrectly assumed that every node would have an IPv4 address~~ - this doesn't apply to bridges~~; * we counted relays when we had already fallen back to non-preferred addresses. This likely affected ~~bridge clients with IPv4 bridges, and~~ clients in small networks.