Mysql support

I've managed to pick the guts out of @chris-blay's [mysql fork](https://github.com/chris-blay/fileconveyor), and get it up to date with Master and it seems to work OK. Have also added support for Rackspace UK endpoints, as per @chrisivens' fork too. 

Hope this is useful for some peeps. I'm by no means a Python expert, so please feel free to tell me where I might be going wrong!

I'm also hoping to add support for mysql in the [Drupal CDN module](http://drupal.org/project/cdn) today, so will shout in the relevant place when that's done.