DTMF hooks: Leaving channels need to push any collected digits into the bridge.

Any partially collected DTMF digits for a DTMF hook need to be pushed into
the bridge when a channel leaves the bridging system as if there were a
timeout.

Review: https://reviewboard.asterisk.org/r/4199/
........

Merged revisions 428601 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@428602 f38db490-d61c-443f-a65b-d21fe96a405b
test_channel_feature_hooks.c: Fix unit test for DTMF hooks.

Fix the failing /channels/features/test_features_channel_dtmf unit test.

DTMF emulation does not work without a stream of packets to prod the
emulation code.

Review: https://reviewboard.asterisk.org/r/4199/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@428604 f38db490-d61c-443f-a65b-d21fe96a405b