Change schema query to involve the use of an optional schema parameter.

Change schema query to involve the use of an optional schema parameter.
This change is done in such a way as to allow the driver to continue to
function with older databases which don't have these features.
(closes issue #16000)
 Reported by: jamicque
 Patches:
       20091002__issue16000.diff.txt uploaded by tilghman (license 14)
       20091002__issue16000__1.6.1.diff.txt uploaded by tilghman (license 14)
 Tested by: jamicque

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@222309 65c4cc65-6c06-0410-ace0-fbb531ad65f3