Allow customizing errors processing in `BaseModelFormSet.validate_unique()`

Django Internals
1

BaseModelFormSet.validate_unique() ​doesn’t offer a way to customize errors for instance to provide a more specific message or add the error message to a specific field.

I propose to fix this problem by adding two process_unique_error and process_date_error that get the form, fields and values as parameters.

I wrote a simple patch to fix this issue

2

I’m upping this topic because I think it’s an important accessibility issue. current validate_unique produces utterly unspecific errors which should be handled in a better manner.