Change in simplejson encoder/decoder imports needed

[sinejoe]

Reference the following Django trac: http://code.djangoproject.com/ticket/13526

Current master of this repo imports JSONEncoder and JSONDecoder directly which results in an error that the JSONDecoder object has no attribute object_pairs_hook.

Modifying models.py and parser.py according to the example code in the Django ticket resolves this issue.

[rbdcti]

+1 on this. running into this issue as well