I'm facing issue with making request of type `ResponseContentType.Blob` and getting error message in case of failed call.

The code is pretty simple:

```
 let headers = new Headers({'Content-Type': 'application/json'});
 let options = new RequestOptions({headers: headers, responseType: ResponseContentType.Blob});

 return this.http.post('url', data, options)
      .subscribe(res => ..., err => console.log(err.json()) /* the problem is here */);

```

So having fully clarify JSON as server response in case of error but I can't access it: `err.json()` returns `Blob {size: 194, type: "application/json"}` only data.

How to access response data? I can't change `ResponseContentType`to smth else as I expect file in case of success request.