Fixed #6941 -- When logging a user out, or when logging in with an existing

session and a different user id to the current session owner, flush the session
data to avoid leakage. Logging in and moving from an anonymous user to a
validated user still keeps existing session data.

Backwards incompatible if you were assuming sessions persisted past logout.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8343 bcc190cf-cafb-0310-a4f2-bffc1f526a37