The cookie check should check that Django's cookie is set

[christianp]

A common problem is that I accidentally set SESSION_COOKIE_SECURE = False when I put debug mode on, and then I get weird errors because the launch goes ahead, thinking cookies can be set, but it only checked pylti1p3's cookie, not Django's.

We should check that the request also includes Django's session and CSRF cookies, and document that if they're not set you should check the *_COOKIE_SECURE settings.