Bug 12630: Prioritizing "Hold starts on date" -holds causes all other holds to be...

Bug 12630: Prioritizing "Hold starts on date" -holds causes all other holds to be prioritized as well!

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-- REPLICATE LIKE THIS --
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0. Enable AllowHoldDateInFuture-system preference!

1. Select a biblio with some holds.
2. Place a hold with the "Hold starts on date"-attribute set to future.
3. More the specific hold up on the priority queue.
4. Add another normal hold, observe how it is prioritized with the "Hold starts on date"-hold, leaving old holds to the prioritization queue tail.

Unfair eh?

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>