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* Remove previously undocumented ``CorsModel`` as it was causing migration
issues. For backwards compatibility, any users previously using ``CorsModel``
should create a model in their own app that inherits from the new
``AbstractCorsModel``, and to keep using the same data, set the model's
``db_table`` to 'corsheaders_corsmodel'. Users not using ``CorsModel``
will find they have an unused table that they can drop.
* Make sure that ``Access-Control-Allow-Credentials`` is in the response if the
client asks for it.