XD-1102: message stores benchmark

Arguably a very dumb micro benchmark with a lot of overhead, but that overhead is constant for each test.

Be sure to cherrypick 8737db5 only if/when merging, as this builds on top of #416

![screen shot 2013-11-21 at 15 28 27](https://f.cloud.github.com/assets/313494/1592353/dda619da-52b9-11e3-8fca-bd652c34e7d0.png)