Bug 8365: Followup Force DateTime type for the datedue variable

Bug 8365: Followup Force DateTime type for the datedue variable

Signed-off-by: Broust <jean-manuel.broust@univ-lyon2.fr>
I tested one more time on a sandbox but I confirm the problem:
the due date doesn't change when you renew more than one time
with syspref renewalperiodbase turned on: "the old due date of
the checkout". The due date should change any time.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Added signed-off line and problem description from bugzilla.
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>