Bug 11947 - renumber reserves when hold is confirmed

Bug 11947 - renumber reserves when hold is confirmed

Currently when a reserve is moved to "waiting" status because it's
acknowledged on checkin, the reserve priorities aren't renumbered. This
causes things to go a bit haywire in the UI, in particular, some
reserves can unjustly end up with priority 1 when they shouldn't. It
also seemed to mess with the logic of who should get it next, but I
didn't look too closely at that.

This patch forces a renumbering so that all the priorities remain
copacetic.

Test plan:
* have a few borrowers, say 4.
* have a biblio with a single item (you can scale this up, it should
  work just the same.)
* issue the item to borrower A
* have borrowers B, C, and D place a hold on the item
* return the item, acknowledge that it'll be put aside for B.
* view the holds on the item.
Without the patch:
* the hold priorities in the UI end up being "waiting, 2, 1" when they
  should be "waiting, 1, 2".
* in the database "reserves" table, they're really "0, 2, 3" when they
  should be "0, 1, 2".
With the patch:
* the hold priorities in the UI end up being "waiting, 1, 2"
* in the database, they're "0, 1, 2"

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Test plan confirms that the problem exists and that the patch corrects
it.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script, especially t/db_dependent/Reserves.t.
Improves priority calculation.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 95056d17b715b74e3f7149d60e12d5a365d70eeb)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>