Acq: When invoice-building with embedded search, allow control of results list

Previously, a results list could accumulate under inconsistent
conditions.  You'd get an accumulating results list if you were pressing
enter after successful searches, but your results lists would clear if
you actually clicked the Search button.  Worse, searches yielding empty
result sets would *appear* to clear your result list, but subsequent
sucessful searches would restore what was there before.

This is the "missing commit" that makes the behavior consistent and
togglable.

Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>