Cache open-ils.fielder results by locale

Cache open-ils.fielder results by locale

The problem was particularly visible in search facets, but existed
before: the cache key used for fielder results did not take locale into
account, so on a multi-locale system the first locale won and populated
the cache for all other locales.

Use a session locale if provided, otherwise default to the locale set in
opensrf.xml

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>