title: MongoDB GridFS Python download_to_stream_by_name throws 'unicode' object has no attribute 'write'
body: <p>When using the PyMongo driver for MongoDB, I'm able to upload images to GridFS successfully using bucket.upload_from_stream(filename, address). It's very straightforward and has no complications.
  But when I try to retrieve that same data using <code>bucket.download_to_stream_by_name(filename, address)</code>, with the second parameter as destination, it throws an error:</p>
  
  <pre><code>AttributeError: 'unicode' object has no attribute 'write'
  </code></pre>
  
  <p>Why is this happening? How do I set the location I want to save my files at?</p>