Search clicked /and/ preceding sf values

When looking for authority records to control a bib field, we currently
search using exactly, and only, the subfield that was clicked.  This
commit changes that so that the full field up to and including the clicked
subfield is used in the simple authority heading search we perform to find
the best-match (pivot) authority record.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>