Fixed/improved release note for refs #13147; thanks Loic.

  ``pk`` parameter in ``params`` for backwards compatibility.

* ``UserCreationForm.errors_messages['duplicate_username']`` is no longer used.

  If you wish to customize that error message, use

  ``User.error_messages['unique']`` instead.

  If you wish to customize that error message, :ref:`override it on the form

  <considerations-regarding-model-errormessages>` using

  ``Meta.errors_messages['unique']`` or, if you have a custom user model, use

  the ``'unique'`` key in the :attr:`~django.db.models.Field.error_messages`

  option of the field designated by

  :attr:`~django.contrib.auth.models.CustomUser.USERNAME_FIELD`.

.. _deprecated-features-1.8: