Bug 8251 - Patrons get incorrectly debarred

Bug 8251 - Patrons get incorrectly debarred

Patrons get incorrectly debarred because of the use of Datetime->delta_days
wich happens to always return a positive number.

Also changed the use of Datetime->truncate function so it follows the docs,
using 'day' instead of 'days' (which is used in DateTime::Duration).

This patch has been tested against master.

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>