bug 1710 and 1739: two new sysprefs (DB rev 092)

bug 1710 and 1739: two new sysprefs (DB rev 092)

As part of fixing hold request bugs 1710 and 1739,
two new system preferences are defined:

AllowOnShelfHolds: YesNo, default value OFF
  * if ON, allow item-level hold requests to be
    placed for available items that are not on loan

AllowHoldsOnDamagedItems: YesNo, default value ON
  * if OFF, item-level hold requests cannot
    be placed on items that are marked damaged.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>