make existing code Py3 compatible (WIP)

This effectively makes `vsc-base` require Python 2.6, so be careful when merging this in (EasyBuild, which needs `vsc-base` will only move to Python 2.6 early 2015).

Currently WIP, not all unit tests pass yet with Python3 (but they still do using Python2.6).

Maybe this should include a bump to v2.0?
use `is3` from `py2and3`?