backends: Added CAS2+SAML1 support.

From commit of Kevin Van Wilder <kevin@inuits.eu>
 at Fri Nov 23 16:16:39 2012 -0100
backends: convert the SAML functions to a class
backends: big refactoring of the SAML1.1 code

The previous block seemed too naive, because it would only pick the
elements it expected (sometimes failing due to namespace).
Now, it's half as naive, looking for a valid structure and logging
any errors in the XML structure.