Django-concurrency

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* better support for django 1.9 ( ``TemplateDoesNotExist`` is now in ``django.template.exceptions``
* improved eror message in ``ConcurrencyListEditableMixin`` :issue:`63` :issue:`64`
* fixes :issue:`61`. Error in ``ConditionalVersionField`` (thanks ticosax)
* fixes ``skipif`` test in pypy

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* drop support for django<1.7
* add support for pypy
* new :class:`concurrency.fields.ConditionalVersionField`
* new decorator :class:`concurrency.api.concurrency_disable_increment`
* :class:`concurrency.api.disable_concurrency` is now a noop if applied to a model not under concurrency management

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* fixes :issue:`56` "Can't upgrade django-concurrency to 1.0" (thanks oppianmatt).

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* **BACKWARD INCOMPATIBLE**:: dropped support for Django prior 1.6
* code clean
* fixes :issue:`54` "Incorrect default for IntegerVersionField" (thanks vmspike).
* fixes :issue:`53`. updates Documentation
* :ref:`disable_concurrency` can now disable concurrency in any model
* :ref:`disable_concurrency` is now also a decorator
* **BACKWARD INCOMPATIBLE**:: removed custom backends. ``TriggerVerionField`` can be used with standard Django
* new way to create triggers (thanks Naddiseo)
* new trigger code
* new :attr:`TriggerVersionField.check`.
* new :attr:`TriggerVersionField.trigger_name`.
* new :setting:`CONCURRECY_ENABLED` to fully disable concurrency
* new :setting:`CONCURRECY_MANUAL_TRIGGERS` to disable triggers auto creation fixes :issue:`41` (thanks Naddiseo)

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* Django 1.8 compatibility
* python 3.4 compatibility
* **BACKWARD INCOMPATIBLE** :func:`disable_concurrency` works differently if used with classes or instances
* better support for external Models (models that are part of plugged-in applications)
* fixes issue with TriggerVersionField and Proxy Models (thanx Richard Eames)

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* avoid to use concurrency when selecting all items (select_across)