Debian bug 690524
When sshd passwordauthenication is turned off (key access only)
then DenyHost does not detect the denied log entry. This means
we are not blocking the remote host when multiple attempts are
made to access the local service. We should try to
detect bad connections to key-only systems.

In cases where DenyHosts cannot write to disk, it should not crash.

Consider support for IPv6

Set up new sync server.

Add support for IPFW on FreeBSD.

Add persistent IPTABLES rules.

Filter out bad IP addresses. Do not allow host names or other invalid IP
addresses.

