Fix DST calculation, and fix bug in calculation of whether conf has started yet or not

(Closes issue #12292)
 Reported by: DEA
 Patches: 
       app_meetme-rt-dst-sched-fix.txt uploaded by DEA (license 3)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@114617 65c4cc65-6c06-0410-ace0-fbb531ad65f3