Unfortunately the Python 2 `raise` syntax is not supported in Python 3.3 and not all 3.4.x versions so we deal with that by using conditional imports and a compatibility layer.
Code now supports Python 2.6, 2.7 and 3.4. PYthon 3.3 isn't support
because of some issues with the parser and the difference between old and
new `raise` syntax.
