Make safe_asterisk work on dash/sh/bash etc.

(closes issue #13111)
Reported by: pabelanger
Patches:
      2008071901_issue13111_safe_asterisk.diff uploaded by mvanbaak (license 7)
Tested by: mvanbaak, pabelanger


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@135061 65c4cc65-6c06-0410-ace0-fbb531ad65f3