Bug 10694 - Allow arbitrary backdating of returns

Bug 10694 - Allow arbitrary backdating of returns

Sometimes libraries need to backdate returns further back in time than
Koha's dropbox mode will allow. The returns backdating will check in an
item as if it had been returned on the specified date, and will reduce
any fine accordingly.

This feature is activated by a new system preference, SpecifyReturnDate.

Test Plan:
1) Apply this patch
2) Check out an item, and backdate the due date by 1 month or so
   * This issue needs to generate a fine
3) Run fines.pl to generate the fine
4) Browse to returns.pl
5) Specify a return date of the day after the specified due date
6) Check the borrowers issue history, you should see the backdated
   return date, rather than today's date
7) Check the fine, it should be reduced to a fine for a single day
   overdue, rather than the previous larger fine.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Barbara Knibbs <BKnibbs@farmingtonlibraries.org>
Signed-off-by: Petter Goksoyr Asen <boutrosboutrosboutros@gmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described, passes tests and QA script.

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