Bug 12086 - Hold priorities incorrect, when waiting status was reversed

Bug 12086 - Hold priorities incorrect, when waiting status was reversed

1) Test record has 1 single item, checked out to patron X
2) Place 3 holds for patrons A, B and C, all title level hold this time
   A, B, C, item branches and staff branch are the same.
3) Return item, confirm hold
4) Confirm item is now waiting for patron A
   Priorities are: A = Waiting, B = 1, C = 2
5) Open patron account of user B, checkout book
   Koha asks: Item X has been waiting for patron A... Revert
   waiting status
   Confirm.
6) Check priorities:
   Hold list shows: A = 1, C = 1
   Database says: A = 1, C = 3
7) Apply this patch
8) Repeat steps 1-6
9) Note the priorities are correct

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Test plan correctly predicts the error and the correction made by the
patch.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>