Setup environment variables for the benefit of child processes and disallow changing them.

(closes issue #14899)
 Reported by: jmls
 Patches: 
       20090916__issue14899.diff.txt uploaded by tilghman (license 14)
 Tested by: jmls


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@266385 65c4cc65-6c06-0410-ace0-fbb531ad65f3