Make compatible with the r4032login module

(Not this includes the commit from #34 as it won't work without. That PR should be reviewed/merged first.)

The [Redirect 403 to User Login](https://www.drupal.org/project/r4032login) might be useful to redirect the user straight to Raven when they aren't authenticated, rather than having to go to an intermediate "You need to log in" page. This should fix the incompatibilities.