[dev] unserialize in Auth.php

[Chuck Hagenbuch]

Quoting Jan Schneider <jan@horde.org>:

> Chuck, you reintroduced the @ before the unserialize call in Auth.php some 
> time ago. But I couldn't reproduce when the error message appears again. 
> Even not with sql authentication as you stated.

When the browser was sending an old cookie to the site, even though cookies 
were disabled, Secret::setKey() was trying to use cookies. I've fixed it to 
check for the session cookie specifically, and that seems to work.

-chuck

--
Charles Hagenbuch, <chuck@horde.org>
"A dream which helps you to live your reality with dignity
 and justice is a good dream." - Tariq Ramadan