Documentation about import_string unclear

[Joachim Jablon]

I found about import_string and import_by_path from django.utils.module_loading, and read their doc :
​https://docs.djangoproject.com/en/dev/ref/utils/#module-django.utils.module_loading

I have the feeling that the example is not chosen wisely as :

• import_string raises an ImportError
• but it replaces import_by_path that used to raise an ImproperlyConfigured error
• And in the example, the function is used to load the ImproperlyConfigured class.

It may leave the fast reader or the beginner under the impression that this function returns an error when called with incorrect parameters. Or at least serious doubts.

(Additionaly, transition code could be provided but that's not as important)

[Tim Graham]

If we replaced the example with something like: ValidationError = import_string('django.core.exceptions.ValidationError') would that address your concerns?

[Tim Graham <timograham@…>]

In c501662f3c3f03876effcf3ede94922c0cec43bd:

Fixed #22618 -- Improved import_string example.

Thanks ewjoachim for the sugggestion.

[Tim Graham <timograham@…>]

In 0bb90de869303f4e0fc9479391fde7c68b4088a0:

[1.7.x] Fixed #22618 -- Improved import_string example.

Thanks ewjoachim for the sugggestion.

Backport of c501662f3c from master