Allows keeping response errors in production mode with sails.config.keepResponseErrors

[alivesay]

IMHO the current behavior in response handlers of clearing the body in production mode should be optional, hence the proposed sails.config.keepResponseErrors here.

Consider the case of a waterline validation error from a model backing a REST operation, one could return a 400 with a list of validation failures:

if (err && err.code === 'E_VALIDATION') {
  return res.badRequest(err.invalidAttributes);
}

The docs here for res.badRequest() say "For requesters expecting JSON, this response includes the 400 status code and any relevant data sent as validationErrors." Well, this isn't true -- in production mode response body is cleared regardless of req.wantsJSON.

Thoughts?

[jpwilliams]

+1. I'd love this functionality.

[sgress454]

Looks good, thanks Andrew! Would you mind adding some docs for it here?

[alivesay]

Done. Thanks all.