Adding support for pushing to the front of the hold queue with a cut_in_line

Adding support for pushing to the front of the hold queue with a cut_in_line
boolean field.  Setting this on an action.hold_request will cause the hold
to sort to the top of the queue in calls to open-ils.storage.action.hold_request.nearest_hold,
which is used to capture holds in priority order.

Currently, this field sorts /after/ the hold proximity.  When strict FIFO
holds are implemented, this sort will go to the front of the line, followed
by request_time and then proximity.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@14509 dcc99617-32d9-48b4-a31d-7c20da2025e4