Issue #410: fail2ban logging to file and/or syslog, or not at all

This adds logging for the fail2ban module, of all failed logins that it handles, and all clients that are denied because of a cached failed login.

We add a third (optional) parameter for the fail2ban module - 
"file" - log to file
"syslog" - log to syslog
"both" - log to both file or syslog
anything else, or omitted - current behavior, no logging

Most of the actual logging code is copied almost verbatim from the adminlog module.

I'd really like to add admin commands to show the current cache, remove 1 host, or clear all... but that's quite a bit beyond my c++ konwledge (which is effectively none).