Fixed typo in topics/http/sessions.txt.
Fixed #15179 -- middlewares not applied for test client login()

Requests made with django.test.Client.login() and logout() respect
defaults defined in django.test.Client instantiation and are processed
through middleware.

Thanks to Loic for the reviews.
Fixed #21361 -- allowed access self.value() from SimpleListFilter lookup

Reviewed by Chris Medrela.
Fixed the base class note in the Date Views docs.
fixed typo in builtins.txt
Merge pull request #1943 from jantokhine/master

fixed typo in builtins.txt
Added more examples to the get_object_or_404 documentation.
Recommended setuptools in the reuseable app tutorial.

setuptools has merged with distribute.
Changed shortcuts from being a package to just being a module
Use `classmethod` as a decorator.
Fixed #20867 -- Added the Form.add_error() method.

Refs #20199 #16986.

Thanks @akaariai, @bmispelon, @mjtamlyn, @timgraham for the reviews.
Removed Form._errors from the docs in favor of the add_error API.