Make better use of the unregister_server function. Straighten out uses of the register_lock. Add debug output when unregistering was successful.
Small comment fixes. Also made a success message in _handle_server_conn_request_helper conditional on the actual success of the connection to the "client" (i.e. host connecting into the TCP relay in order to reach a node behind a NAT/firewall).
Add note on how to improve the handling of cases where a client requests to be forwarded, but the server becomes unavailable.
Added notes on how to improve the code.

This includes feature requests as well as hints to make the code
more stable, e.g. by using additional timeouts, closing rogue
connections, not starting threads unless the client and server
are both notified they are connected, etc.
Merge branch 'beta' into improve-tcp_relay.r2py
Make updatetime() try the allowed UDP ports (rather than hardcode one).

* Make the time library return getruntime() if no NTP server can be
reached. Make logmsg() use time.time_getunixtime().
* Correct the usage string and "Starting" log message.
Merge branch 'beta' into improve-tcp_relay.r2py
Merge branch 'improve-tcp_relay.r2py' into minimal-clean-alpha-release