Add a non-invasive API for application level manipulation of T38 on a channel....

Add a non-invasive API for application level manipulation of T38 on a channel. This uses control frames (so they can even pass across IAX2) to negotiate T38 and provided a way of getting the current status of T38 using queryoption. This should by no means cause any issues and if it does I will take responsibility for it.
(closes issue #11873)
Reported by: dimas
Patches:
      v4-t38-api.patch uploaded by dimas (license 88)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@103799 65c4cc65-6c06-0410-ace0-fbb531ad65f3