[PATCH 5 of 7] setup: support executing with python3 including 2to3

[Sjujskij Nikolaj]

>> Wouldn't
>>     print("warning: IronPython detected (no bz2 support)")
>> work everywhere?
> Yes, that's one typical Py2- and Py3-compatible way of using print.
  Excuse me guys, but that would break Pythons 2.{4,5}.*, or do I miss
something? And `from __future__ import print_function` wouldn't work
there neither.