Added new channel command FTDM_COMMAND_SET_POLARITY
         ftmod_wanpipe - Added support to enqueue polarity events on FXO lines
	 ftmod_wanpipe - Added support to set polarity on FXS lines
	 ftmod_analog - Added support to answer and hangup FXO lines on polarity reverse
	 ftmod_analog - Added support to reverse polarity in the FXS line on answer and hangup
	 mod_freetdm - Added parameters answer-on-polarity, hangup-on-polarity and polarity-delay
                       to enable those analog features