Differences in JSON error handling

[ryanblock]

Not sure what the history is here, but there's currently differentiation in handling JSON errors:

• get: err.body = isJSON? JSON.stringify(result) : result.toString() (code)
• !get: err.body = result (code)

These should probably be the same – either is fine imo, but given the nature of the library, probably passing the parsed version back prob makes more sense.