Python 3.3 compatibility

Those changes make tox pass for Python 3.3 and 2.7 as well the example usage code works for Python 3.3. It still could be compatible with 2.6. I had to hardcode the version to avoid execfile - that's something incompatible if any user-code checks version value.

I still need to finish porting "my" Facebook gallery application to Python 3.3 to get some real usage cases, but those commits provide working Python 3.3 support. Tests like to pass strings while real usage gets bytes from requests so there still may be some str/bytes exceptions left.