When a new logout session is received, save old session ids

When a new logout session is received, save old session ids

When a new login session is received and an existing session
exists in logout, save the old session IDs.

These will be included in the sessions to logout of the SP.

This will ensure that if the user clears their cookie cache,
for example, that any previous sessions will also be logged
out.

https://fedorahosted.org/ipsilon/ticket/64

Signed-off-by: Rob Crittenden <rcritten@redhat.com>