ACQ support for two-step vandelay imports

ACQ support for two-step vandelay imports

If a lineitm is loaded into a queue via ACQ+Vandelay and a later attempt
is made to load the record into the catalog via ACQ+Vandelay, the
attempt will fail, because ACQ+Vandelay treats all
not-yet-fully-imported lineitems as new to vandelay.  This change
inspects lineitems at vandelay processing time to determine if they are
already linked to a VL record or if a new one is needed.  It also
removes the requirement that a queue be provided when all records in
process are already linked to a VL record (which already lives in a
queue).

Signed-off-by: Bill Erickson <berick@esilibrary.com>