django/django — pull request #2235 by loic (2014-02-03 18:40:13+00:00)
Title: Fixed 16192 -- Made unique error messages in ModelForm customizable.

Overriding the error messages now works for both unique fields, unique_together
and unique_for_date.

This patch changed the overriding logic to allow customizing NON_FIELD_ERRORS
since previously only fields' errors were customizable.

Refs #20199.