Added additional behavior to Poll

>>> poll.choice_set.filter()[0].delete()
>>> poll.choice_set.count()
0

>>> for choice in poll.choice_set.all():
...   print Poll.objects.get(pk=choice.poll.id).question,
choice.choice_text
...
Which 3D software did you like? Blender
Which 3D software did you like? Houdini