Allow tonelist as argument to ReadExten.

ReadExten already supported playing a tonezone from indications.conf.
It now has the ability to use a tonelist like 440+480/2000|0/4000

(closes issue #15185)
Reported by: jcovert
Patches:
      app_readexten.c.patch uploaded by jcovert (license 551)
Tested by: qwell
Patch modified by me, to maintain backwards compatibility.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@234776 65c4cc65-6c06-0410-ace0-fbb531ad65f3