Entirely through my own stupidity, I managed to corrupt the Arabica subversion repository. By sheer good luck, I'd been using Bazaar as my front-end client, and so had a clone of the entire repository sitting in my working directory. Accordingly, the Arabica source code is now housed in a Bazaar repository.
The repository can be browsed and you can grab your own working copy over HTTP using
bzr branch http://jezuk.dnsalias.net/arabica-bzr/trunkWrite-access using
bzr+sshis available on request.