Update UPGRADE.txt and CHANGE for CDR functionality changes.

Updated the UPGRADE.txt and CHANGES file stating that CDR records will not be explicity
written unless cdr.conf exists and is configured.

(closes issue #17373)
Reported by: wdoekes
Tested by: pabelanger

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@267624 65c4cc65-6c06-0410-ace0-fbb531ad65f3