Fix holding lib for certain distribution svrs

On a serial virtual record (svr), the holding lib is expected to be
just an ID.  In one logic branch, Search/Serial.pm was attaching the
entire aou object, and we should instead attach just the ID of this
object.

Signed-off-by: Dan Wells <dbw2@calvin.edu>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>