Python 3.3 support

[Nikoli]

Please add support for python-3.3: my collectd server does not have python2. I checked every dep from requirements.txt, most of them support python-3.3 already, there are only 2 minor blockers:

1. PyRRD https://code.google.com/p/pyrrd/issues/detail?id=28
   but python-rrdtool has support for python3 https://github.com/commx/python-rrdtool
   Why are you using both python-rrdtool and pyrrd?

2. nosy is old (latest version from 2011-09-16) and supports python2 only. But it is used only for tests and is optional.