Name conflict if tracked model has field named "instance"

[shemigon]

Problem

If a tracked model has a field called instance, creating a instance of the model throws

TypeError: Model.__init__() got multiple values for argument 'instance'

See issue https://github.com/jazzband/django-model-utils/issues/633

Solution

Removed instance argument from the new model init method and used args[0] instead.

Commandments

• [x] Write PEP8 compliant code.
• [x] Cover it with tests.
• [x] Update CHANGES.rst file to describe the changes, and quote according issue with GH-<issue_number>.
• [x] Pay attention to backward compatibility, or if it breaks it, explain why.
• [x] Update documentation (if relevant).

[livenson]

Hi, are there any plans to get this change into the upstream? We are being hit with it and wondering about prospective.

[shemigon]

@livenson I'm not a maintainer of the repository. I created this PR a while ago and it's been unnoticed ever since.