implement transfer functionality in chan_skinny

(closes issue #9939)
Reported by: wedhorn
Patches:
      transfer_v6.diff uploaded by wedhorn (license 30)
      chan_skinny-transfer-trunk-v10.txt uploaded by DEA (license 3)
      chan_skinny-transfer-trunk-v12.txt uploaded by mvanbaak (license 7)
Tested by: DEA, wedhorn, mvanbaak


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@125096 65c4cc65-6c06-0410-ace0-fbb531ad65f3