add session counter and make all sessions hang up elegantly on shutdown

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@1788 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/switch_channel.c

@@ -83,6 +83,7 @@ static struct switch_cause_table CAUSE_CHART[] = {
 	{ "PROTOCOL_ERROR", SWITCH_CAUSE_PROTOCOL_ERROR },
 	{ "INTERWORKING", SWITCH_CAUSE_INTERWORKING },
 	{ "CRASH", SWITCH_CAUSE_CRASH },
+	{ "SYSTEM_SHUTDOWN", SWITCH_CAUSE_SYSTEM_SHUTDOWN },
 	{ NULL, 0 }
 };