AuthMemCookie: Delete the session cookie when deleting the session.
AuthMemCookie: Delete the session cookie when deleting the session.

Update issue 219
Status: Fixed
This patch implements deletion of the AuthMemCookie session cookie when
logging out.

rchavik/simplesamlphp,rchavik/simplesamlphp,rchavik/simplesamlphp,rchavik/simplesamlphp