Update admin.py

django.contrib.admin.options.py:ModelAdmin.change_view has following signature(Django 1.4&1.5):

def change_view(self, request, object_id, form_url='', extra_context=None):

Currently passing extra_context dict without explicit naming( extra_context=extra_context) actually works as implicit form_url=extra_context. This issue blocks submiting Worker and Task admin forms.