Refactor tor to support the new tor-fw-helper protocol.

Add handle_fw_helper_output(), a function responsible for parsing the
output of tor-fw-helper. Refactor tor_check_port_forwarding() and
run_scheduled_events() accordingly too.

We now issue warnings when we get control output from tor-fw-helper,
and we log the verbose output of tor-fw-helper in LOG_INFO.

Conflicts:
	src/common/util.c