save “stay_logged_in” in the session

Since sessions are rebuilt, e.g. when you try to post a blank
comment and therefore receive an error message, the session will
be overwritten without the old max_age.

mediagoblin/auth/views.py

@@ -89,7 +89,7 @@ def login(request):
             if user:
                 # set up login in session
                 if login_form.stay_logged_in.data:
-                    request.session.max_age = 30 * 24 * 60 * 60
+                    request.session['stay_logged_in'] = True
                 request.session['user_id'] = unicode(user.id)
                 request.session.save()