Deadlock between dahdi_exception() and dahdi_indicate().

Deadlock between dahdi_exception() and dahdi_indicate().

There is a deadlock between dahdi_exception() and dahdi_indicate() for
analog ports.  The call-waiting and three-way-calling feature can
experience deadlock if these features are trying to do something and an
event from the bridged channel happens at the same time.

Deadlock avoidance code added to obtain necessary channel locks before
attemting an operation with call-waiting and three-way-calling.

(closes issue #16847)
Reported by: shin-shoryuken
Patches:
      issue_16847_v1.4.patch uploaded by rmudgett (license 664)
      issue_16847_v1.6.2.patch uploaded by rmudgett (license 664)
      issue_16847_v1.8_v2.patch uploaded by rmudgett (license 664)
Tested by: alecdavis, rmudgett

Review: https://reviewboard.asterisk.org/r/971/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@291643 65c4cc65-6c06-0410-ace0-fbb531ad65f3