Make Flake8 runner Python 3-compatible.
Add support for Python 3.3 in tox and README.
Run py33 in Travis.
Merge branch 'master' into python3
Merge branch 'master' into python3
Merge branch 'master' into python3
Merge branch 'master' into python3
use list comprehension instead of filter call as suggested by 2to3 script