Properly extract channel variables for the SendFAX/ReceiveFAX Stasis messages

By the time something extracts the pointers from ast_json_pack, the channels
will already be disposed of. This patch properly pulls the information out of
the variables and packs them into the JSON blob.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@392607 65c4cc65-6c06-0410-ace0-fbb531ad65f3