Fixed the attribute discovery for Django 1.5

- It was returning all attributes of objects when not specified
  `fields`, which would include even private and protected
attributes/methods. Particularly on Django 1.5, when relations are
cached in private methods it was causing a circular loop when dumping
objects with relation.
Trying to fix CircleCI to run the tests for piston
Trying to fix CircleCI to run the tests for piston
Trying to fix CircleCI to run the tests for piston
Trying to fix CircleCI to run the tests for piston
Merge pull request #10 from lucmult/fix-max-recursion

Fixed the attribute discovery for Django 1.5