[SAC] fail2ban based trac spam filter

[Sandro Santilli]

FYI, on trac.osgeo.org I've added a trac-specific fail2ban
jail configuration to ban hosts which attempt to create
spam-looking wiki pages.

Right now the filter is very simple, it won't catch every
spam attack and the ban will only last 10 minutes. I'm a bit
afraid about testing it as I suspect (but didn't test to confirm
that being banned by fail2ban would mean being banned from any
service, including ssh).

Markus: if you have availability of multiple IP addresses and
want to test it, see /etc/fail2ban/filter.d/osgeo-trac.conf
for what I'm up to.

--strk;