Try to use Python's built-in json module.

According to the Django 1.5 [release notes](https://docs.djangoproject.com/en/dev/releases/1.5/#system-version-of-simplejson-no-longer-used),

  >Django 1.5 deprecates django.utils.simplejson in favor of Python 2.6’s built-in json module.

In Django 1.7a2, importing `django.utils.simplejson` raises the exception:

    ImportError: cannot import name simplejson

These modifications attempt to import Python's built-in json module, and if that fails, to attempt to use `django.utils.simplejson`.