Bug 10859: Alert if a borrower already has an issue for the same biblio

Bug 10859: Alert if a borrower already has an issue for the same biblio

This patch adds a new system preference, AllowMultipleIssuesOnABiblio.

If this system preference is OFF, an alert is raised if a patron
tries to check out an item even when they already have a different
item checked out from that bib.

The librarian can force the checkout anyway.

It doesn't alert the librarian if the biblio is a subscription

Test plan:
1. Create a biblio with at least 2 items
2. Checkout the first item for a borrower
3. Set syspref AllowMultipleIssuesOnABiblio to OFF.
4. Try to checkout the second item with the same borrower. A message
should appear telling you that this borrower already borrowed an item
from this biblio.
If you have the permission 'force_checkout' You should also see two
buttons to confirm (or not) the checkout
5. Click on 'No'. The checkout is not done
6. Repeat step 4 and click 'Yes', the checkout is done.
7. Return the second item.
8. Set syspref AllowMultipleIssuesOnABiblio to ON
9. Try to checkout the second item with the same borrower. This time
the checkout is done without warnings.

Followed test plan. Works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
All tests and QA script pass, works well. Tested:

* Permission to override
  * check out a second item from a record with subscriptions works
  * check out a second item from a 'normal' record is warned about,
  but can be done

* No permission to override
  * subscription item: can be checked out
  * normal item: can't be checked out

* Feature turned off
  * Check out never warns/blocks

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