Code review comment for lp://staging/~mbp/launchpad/feature-modulus

https://bugs.launchpad.net/launchpad/+bug/666544 (which I didn't have access to when i wrote this offline) suggests that I need to test it for anonymous requests, and secondly that we can do a follow-on thing, or a separate scope, that activates things for a percentage of sessions, which will help for anon users.