improve performance of multi-class searches

improve performance of multi-class searches

Backport of trunk commit 18233.

For as yet unknown reasons, Postgres sometimes uses
nested loops instead of hash joins when joining subqueries
in a multi-class bib search.  This can result in searches
such as "author:rowling title:harry potter" never completing.

Removing the interior limit clause can both speed up the query
and make search results more accurate when combining queries
of two or more common words.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
git-svn-id: svn://svn.open-ils.org/ILS/branches/rel_1_6@19263 dcc99617-32d9-48b4-a31d-7c20da2025e4