Bug 8769: Allow SIP2 return backdating

Currently Koha's SIP server ignores the return date part of an 09 ( aka
CHECKIN ) message. Koha should backdate a return, and remove
fines accordingly.

Signed-off-by: Benjamin Rokseth <benjamin.rokseth@kul.oslo.kommune.no>

Works as notified, second date field in SIP checkin (return date) is
used as return date. Return shows up in history with correct date.

Comments:
 - patron is fined if return date is before issue date, but that
   is largely irrelevant anyway.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 8769: (follow-up) remove unnecessary module import

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 8769: (follow-up) undo change to value of $today

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