Added python3 support

Various relatively small fixes to get it working on python 2 and 3. `0o777` instead of `0777` as octal syntax, for instance. `print(xyz)` instead of `print xyz` in the doctest.

At the same time I added some adjustments for buildout 2.x (bin/sphinx would contain `sys.exit(sys.exit(...))` as buildout 2 itself already adds the `sys.exit()` now).

I kept the tests running. I had to add an extra renormalizer (copied from zc.buildout) to suppress messages from newer setuptools.

I tested it (bootstrap, bin/buildout, bin/test) with python 3.3, 2.6 and 2.7. 2.5 already fails because of some setuptools thingy.

(Note: also accept my other pull request before doing any release as there's a .rst error in `usage.txt` now which breaks the pypi page rendering).