Work around transaction search timeouts in the client

As promised, here's a client-side fix to the transaction timeout search issue in #46. It works by catching the `422 Unprocessable entity` responses and retrying with two smaller requests -- recursively.

![brooms](https://f.cloud.github.com/assets/118362/1696050/d72f4e5a-5ebc-11e3-92c3-50f05e5d7cf7.jpg)

I believe #55 is the right solution, but this would work too.