Add backupdeleted option to app_voicemail

(closes issue #10740)
Reported by: ruffle
Patches:
      app_voicemail.diff uploaded by ruffle (license 201)
      10740-voicemail.diff uploaded by qwell (license 4)
      20080113_bug10740.diff.txt uploaded by mvanbaak (license 7)
Tested by: blitzrage, mvanbaak, qwell


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@98889 65c4cc65-6c06-0410-ace0-fbb531ad65f3