Fix the get_chunk response. It was sending UTF-8 encoded responses, making
the results all wrong. The problem was that we were using Requests' response
text field, whereas we're better using the content field.

- Add some debug printing
Changed import policy to be Python3-compatible.

- In Py3k upload_chunk passes chunk as bytes. So now the driver uses StringIO
  in Python 2 and BytesIO in Python 3

- Change the syntax of the tinys3 import for python 3. Luckily the new syntax
  is valid in both versions

- Add a try/catch in get_file