#23 Deprecation warning with Python 2.6

[Colin McPhail]

It would be good to check the version of Python in use before importing the Sets module since it gives a deprecation warning with Python 2.6:
$ python test_all.py
/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/sets.py:85: DeprecationWarning: functions overriding warnings.showwarning() must support the 'line' argument
stacklevel=2)
** DeprecationWarning: the sets module is deprecated
Zero delay behavior ... ok
...

[Jan Decaluwe]

Solved in development.