Add headers from SIPAddHeader to outbound REFER requests.

Add headers from SIPAddHeader to outbound REFER requests.

This is a patch from kkm from review board.

This is useful for adding headers to REFER requests that
emanate from a Transfer() dialplan application call.

This also fixes some uses of the Referred-by header, removing
an extra set of angle brackets.

I've modified the reporter's original patch to not require
any additions to the sip_refer header and to just remove the
referred_by_name from sip_refer since it is no longer needed
or used.

(closes Issue ASTERISK-17639)
reported by Kirill Katsnelson
Patches:
	019059-sip-refer-addheaders-trunk-353549.diff
	uploaded by Kirill Katsnelson (license #5845)

Review: https://reviewboard.asterisk.org/r/1159

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@370691 65c4cc65-6c06-0410-ace0-fbb531ad65f3