Fixed: Using AuthSessionFS sessions will always be expired (bug#10617).
Squashed commit of the following:

commit af531787fadc83afdc7329a50076248abce3584e
Author: Michiel Beijen <michiel.beijen@gmail.com>
Date:   Tue Jul 8 21:58:28 2014 +0200

    Correctly handle UserSessionStart on AuthSessionFS

    On AuthSessionFS the UserSessionStart value was not used.

    This fixes http://bugs.otrs.org/show_bug.cgi?id=10617
    "Using AuthSessionFS, sessions will always be expired"

    Also, I improved the perldoc a little on the data structures
    returned, and added a unit test for this specific bug.

    It might be good to still add some more tests for expired
    sessions.