Support negative filters.

(closes issue #17979)
 Reported by: tilghman
 Patches: 
       20100911__for_blitzrage.diff.txt uploaded by tilghman (license 14)
 Tested by: lmadsen


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@300045 65c4cc65-6c06-0410-ace0-fbb531ad65f3