Authentication Middleware assertion message is only partially correct

[Keryn Knight <django@…>]

Currently, the ​middleware says The Django authentication middleware requires session middleware to be installed. Edit your MIDDLEWARE_CLASSES setting to insert 'django.contrib.sessions.middleware.SessionMiddleware'. which is true, but doesn't expound the need for the session middleware to be before the auth middleware, because it acts on the request.

eg:

MIDDLEWARE_CLASSES = (
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
)

would fail the assertion, where

MIDDLEWARE_CLASSES = (
     'django.contrib.sessions.middleware.SessionMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
)

would pass.

[Tim Graham <timograham@…>]

In 246face20984b70b93751d144760bfd9b45d2c09:

Fixed #22362 -- Improved AuthenticationMiddleware assertion message.

Thanks Keryn Knight.

[Tim Graham <timograham@…>]

In ef3734693277242e98996f591d9acf39e8819441:

[1.7.x] Fixed #22362 -- Improved AuthenticationMiddleware assertion message.

Thanks Keryn Knight.

Backport of 246face209 from master