Django-autofixture

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* Fixed unique constraint for models that have multiple unique_togethers set.

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* Make ``ImageGenerator`` consider the given file storage. Thanks to Andrew
Pashkin for the patch.
* Fixing check for unique constraint during data generation if the field
allows to be nullable. Thanks for Andrew Pashkin for the report and fix.

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* Adding support for django's ``ImageField``. Thanks to Visgean Skeloru for
the patch.

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* Adding ``AutoFixture.pre_process_instance`` method.
* Allow arbitrary keyword arguments for ``AutoFixture.create`` method.
* Fixing ``autofixture.unregister`` function.
* Fixing ``UserFixture.post_process_instance``.

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* Fixing long stated issue with GenericRelation fields. Thanks to StillNewb
for the patch.

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* Supporting Django 1.6.