OPENZAP-238: [freetdm] Several core and gsm improvements

OPENZAP-238: [freetdm] Several core and gsm improvements

* Add error handing in mod_freetdm for ftdm trace failures

* Allow freetdm signaling modules to specify a destroy function

* Added conditional forwarding to the freetdm gsm module
  Just specify the conditional-forwarding-number gsm parameter in freetdm.conf.xml

* Added new 'gsm call' freetdm command for raw GSM calls which can be
  used to enable/disabling network features (e.g call *93) without
  having to resort to use a full originate that requires routing the
  call somewhere when answered

* Miscelaneous cleanup of piggy coding style left over by one of the
  previous authors -_-