Add a hashcompat mode called "legacy", which translates a literal plus sign to a space.

(closes issue #18046)
 Reported by: wdoekes
 Patches: 
       20100930__issue18046.diff.txt uploaded by tilghman (license 14)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@300840 65c4cc65-6c06-0410-ace0-fbb531ad65f3