Asterisk does not hangup a channel after endpoint hangs up.

Asterisk does not hangup a channel after endpoint hangs up.

If the call that the dialplan started an AGI script for is hungup while
the AGI script is in the middle of a command then the AGI script is not
notified of the hangup.  There are many AGI Exec commands that this can
happen with.  The reported applications have been: Background, Wait, Read,
and Dial.  Also the AGI Get Data command.

* Don't wait on the Asterisk channel after it has hung up.  The channel is
likely to never need servicing again.

* Restored the AGI script's ability to return the AGI_RESULT_HANGUP value
in run_agi().  It previously only could return AGI_RESULT_SUCCESS or
AGI_RESULT_FAILURE after the DeadAGI and AGI applications were merged.

(closes issue #17954)
Reported by: mn3250
Patches:
      issue17954_v1.8.patch uploaded by rmudgett (license 664)
      issue17954_v1.6.2.patch uploaded by rmudgett (license 664)
      issue17954_v1.4.patch uploaded by rmudgett (license 664)
Tested by: rmudgett
JIRA SWP-2171

(closes issue #18492)
Reported by: devmod
Tested by: rmudgett
JIRA SWP-2761

(closes issue #18935)
Reported by: nvitaly
Tested by: astmiv, rmudgett
JIRA SWP-3216

(closes issue #17393)
Reported by: siby
Tested by: rmudgett
JIRA SWP-2727

Review: https://reviewboard.asterisk.org/r/1165/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@313545 65c4cc65-6c06-0410-ace0-fbb531ad65f3