Merge pull request #1 from tonysyu/pr/613

Minor cleanups to test
Merge pull request #613 from adamw523/master

support for saving to file-like object in imsave
Remove 2to3.
Add six compatibility module.
Remove is_str and replace by isinstance(..., six.string_types).
Correctly check for string type.
Fix zip.
Fix function code.
Fix iterator.
Fix label casting for numpy 1.7.
fix arraypad
adding main to run tests
Fix im_class access in Python 3.
Fix im_self access in Python 3.
Fix imports under Python 3.
Use int32 for labelling.
Add  to public API.
Space code more readably in transform.
Minor fixes

- Use absolute imports so __main__ examples work
- PEP8: 2 blank lines
Ensure PIL tests run with PIL.