mod_skinny: fix behavior of transfer when target extension falls through to voicemail - keep bridge from dropping out during that operation

We're already avoiding it on sid and jessie; now we're hitting build
failures with it on wheezy.

ref: FS-6811

* Honor the timer name variable

* Added mod_bert::in_sync event when the stream is in sync

* Added BERT stats channel variables

* Check if the channel is going down when out of sync to avoid flagging it
  as out of sync, if the channel is going down it is expected to have some errors

* Improve bert input debug
* Check for SFF_CNG and ignore those frames

* Use digital milliwatt as the test sequence pattern
* Add debug IO files (enabled using bert_debug_io_file variable)

* Calculate sampling error rate over a time window

* Create the following variables to control bert testing behavior:
  bert_timeout_ms - Milliseconds to wait for bert sync before timing out
  bert_window_ms - Window of time to calculate sampling error rate percentage
  bert_max_err - Max percentage of error tolerated before going out of sync
  bert_hangup_on_error - Hangup when error occurs (Timeout or going out of sync)

* commit '9215c938':
  FS-6785 - pass and use sample rate in switch_core_session_get_payload_code()

Merge pull request #38 in FS/freeswitch from ~ALEXDG/freeswitch-event-for-gateway-ping:master to master

* commit '388e9638':
  F-5946 add the patches. if in the sofia gateway config the param pin-monitoring is true, then every ping result raise an sofia::gateway-state event

* commit '6753ccf6':
  Missed one of the variable changes!

if read multi times when waiting for a slow client, then bytes is much shorter than datalen
so it could incorrectly terminate the string and data could be lost