update django-polymorphic repo url

isn't this the right repo for django-polymorphic?
Excluded Django master and Python 2.6 build.

Django master (1.7) has dropped support for Python 2.6.
Merge pull request #365 from regadas/patch-1

update django-polymorphic repo url
Removed some deprecated Django settings.
Removed simplejson alias.
Merge pull request #369 from timgraham/exclude_py26_django_master

Excluded Django master and Python 2.6 build.
Merge pull request #370 from timgraham/deprecated_settings

Removed some deprecated Django settings.
Merge pull request #373 from timgraham/simplejson

Removed simplejson alias.
Added Python 3.3 compatability.