python 3.3 support

I have found that the only obstacle to use djangocms-blog with python 3.3 is django-select2 dependency. It has to be changed to django-select2-Py3. For some strange reason they do not support python 2-3 compatibility in the same package. 
I have changed the dependency in setup.py to check running python version and select django-select2 package accordingly. Seems to work but I am not sure if this is the best solution in this case.