Add support for unittest2.
Add support for unittest2.

Signed-off-by: Raphaël Barrois <8eb3b37a023209373fcd61a2fdc08256a14fb19c@polyconseil.fr>

pombredanne/python-semanticversion,marcelometal/python-semanticversion,rbarrois/python-semanticversion,mhrivnak/python-semanticversion