Add option 'keepstats' which will keep queue statistics during a reload....

Add option 'keepstats' which will keep queue statistics during a reload. (issue #7908 reported by jmls)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@44150 65c4cc65-6c06-0410-ace0-fbb531ad65f3