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Updates ``celery-bungiesearch`` to be compatible with the most up to date version of bungiesearch (1.2.1 as of 8/13/2015).
* The setup and teardown methods in the signal processor reflect the mechanism by which bungiesearch performs signal processing
* Defaults index task to ``CeleryIndexTask`` (no longer required to provide this in settings)
* Bulk delete acts upon primary keys, and not entire instances
* Clean up and increased error handling