Done in https://github.com/chrismedrela/django/commit/16227fb2ee52183acfe03890bd80730a4d6df876. For most objects, `__repr__` method is called; but the cases of `Model` class and `None` are hardcoded. This piece of code has been touched in https://github.com/chrismedrela/django/commit/9332a4f46bf2782fdb42cdf82e946a8a73884aa0 too.

We've decided to merge short and long description, so error messages will be single-line. I think that putting error message on one line and hint on the second one doesn't make sense, so I've decided to come back to one-line errors style (`object_representation: error_message HINT: Hint`, everything in one line).