Bug 4841: biblio-level itemtypes not searchable in advance search by itype

Bug 4841: biblio-level itemtypes not searchable in advance search by itype

Mapping 942$c into itype index along with 952$y; this allows for biblios without any items, but with a biblio-level itemtype to be retrieved in search. This is particularly useful for E-books or Serials without barcoded items.

Signed-off-by: Ian Walls <ian.walls@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit d5a886201cd5e2f7615b92ad727ba136eb105bab)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>