* When "auto_jsonify" is set to True, and responses are returned
  that have explicitly set content types that are not "application/json",
  don't try to JSON encode the response -- return it as is.
   * This makes iterator/generators work correct with APIs (i.e.
     you're streaming back large payloads like images, text, etc.)
* Updated the bundled Swagger UI to 4.17.1
* Added a test to verify the new auto_jsonify behavior.