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.