This patch adds support for a draft proposal for adding Q.850 reason headers to sip messages.

(closes issue #13385)
Reported by: adomjan
Patches:
      sip.conf.sample-trunk20090929-reason_q850.patch uploaded by adomjan (license 487)
      CHANGES-trunk20090929-reason_q850.patch uploaded by adomjan (license 487)
      chan_sip.c-trunk20090929-reason_q850_atoi_fix.patch uploaded by adomjan (license 487)
      sip-q850-hangupcause1.diff uploaded by mnicholson (license 96)
Tested by: adomjan



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@226687 65c4cc65-6c06-0410-ace0-fbb531ad65f3