Fix DTMF blind transfer continuing to execute dialplan after transfer.

Fix DTMF blind transfer continuing to execute dialplan after transfer.

Party A calls Party B.
Party A DTMF blind transfers Party B to Party C.
Party A channel continues to execute dialplan.

* Fixed the return value of builtin_blindtransfer() to return the correct
value after a transfer so the dialplan will not keep executing.

* Removed unnecessary connected line update that did not really do
anything.

* Made access to GOTO_ON_BLINDXFR thread safe in check_goto_on_transfer().

* Fixed leak of xferchan for failure cases in check_goto_on_transfer().

* Updated debug messages in builtin_blindtransfer() and
check_goto_on_transfer().

(closes issue ASTERISK-18275)
Reported by: rmudgett
Tested by: rmudgett

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@340809 65c4cc65-6c06-0410-ace0-fbb531ad65f3