yet another bib ingest knob

yet another bib ingest knob

When enabled, the ingest.assume_inserts_only flag disables
checking several tables for old index data to delete; skipping this
makes a small but noticeable difference when doing an initial bib
ingest with more than one process in parallel.

Note that this flag should not be used when *re*ingesting records
unless you clear the old rows beforehand.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
git-svn-id: svn://svn.open-ils.org/ILS/trunk@17863 dcc99617-32d9-48b4-a31d-7c20da2025e4