The previous approach to reducing index bloat arguably went too far, in
that analytics such as separately catalogued songs for an album were all
simply aggregated together in a single metabib.title_field_entry row,
rather than being added as separated metabib.title_field_entry rows for
each unique value.
To avoid the original problem of exact duplicate rows being inserted, we
now check for an existing matching row before inserting into the index.
A good test record is title "Cello concerto." which results in 1 title
proper row and 4 added entry title rows in metabib.title_field_entry
after this change.