changed "a list or tuple" to "an iterable (e.g., a list or tuple)"
deleted hint from db_index check
added missing 'a'
made error message for DecimalField shorter
quoted some attributes in error message
changed error message when ImageField is in use and Pillow is not installed
small cleanup: indented under-indented line
'swappable user model' -> 'custom user model'
'pointed' -> 'pointed to'
Warning -> Error for check if username is not included in REQUIRED_FIELDS
changed the way requires_model_validation/requires_checks options are handled
imported FieldDoesNotExist directly in _check_ordering
changed mysql backend error message
changed _check_local_fields -- return all errors, not only the first one
changed check of username uniqueness
improvement for 'changed the way requires_model_validation/requires_checks options are handled
second improvement for 'changed the way requires_model_validation/requires_checks options are handled' + docs improvements
improved BaseCommand.check docstring
improved BaseCommand.requires_checks documentation
added tests for GenericForeignKey and GenericRelation