Always attach `body` to response object?

I'm trying to test an image request with tobi and want to check that the body is being sent correctly. Unfortunately, the params that are given for non html/json responses don't contain any way to get at the body (that I can see).

Would there be any problem with always attaching the body at `res.body`, like is currently done with json requests?

I'll code up a pull request if you like this idea.
