If the argument to the system application is quoted, ensure we remove the quotes before trying to execute.

(closes issue #16842)
 Reported by: ip-rob
 Patches: 
       20100310__issue16842.diff.txt uploaded by tilghman (license 14)
 Tested by: ip-rob


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@251877 65c4cc65-6c06-0410-ace0-fbb531ad65f3