Add XML documentation for:

   - WaitForSilence()
   - WaitForNoise()
   - WaitForRing()
   - IVRDemo()
   - DBDel()
   - DBDeltree()

 (issue #13699)
 Reported by: snuffy
 Patches: 
       bug13699_20081016.diff uploaded by snuffy (license 35)
        (With minor changes)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@153747 65c4cc65-6c06-0410-ace0-fbb531ad65f3