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.
Likewise, if /etc/hosts.deny does not exist, that should not make
DenyHost panic or crash.

Add new option to write list of banned IP addresses to a location
such as /etc/blacklist

Consider support for IPv6

Create new sync server.

