Bug 11048: Fix logout redirection for CAS authentication

Bug 11048: Fix logout redirection for CAS authentication

 The logout redirection function after a CAS authentication was misused.
 This patch fixes it, and allows the CAS server to redirect the user back
 to the opac after logout.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>

From the Authen::Cas::Client documentation

logout_url [%args]
         "logout_url()" returns the CAS server's logout URL which can
	 be used to redirect users to end
         authenticated sessions.  %args may contain the following
	 optional parameter:

         *   url => $url

	 If present, the CAS server will present the user
	 with a link to the given URL once the user has logged out.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Change only affects CAS authentication and is correct
according to the module documentation.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>