[Rack] wiki captcha installed

[Danny O'Brien]

It's just the basic "add these two numbers together" default that
comes with ConfirmEdit; I'll start looking into the others next.

I used the Debian/Ubuntu framework for mediawiki-extensions, which
involved plucking a (compatible) package from a later dist --
http://packages.ubuntu.com/oneiric/mediawiki-extensions  and using
dpkg.

I wouldn't do that normally, but the alternative was hand-rolling and
configuring the extension myself (or setting up apt-pinning MADNESS).

Better to keep to the distribution configuration model. The
dependencies are very straightforward, and I'm keeping a
semi-automated eye on for any updates.

d.