Now if we aren't given an explicit port, we always initiate the port search
at 12300 and count upward looking for an available port.

Normally the kernel will assign us a random port, but that's not ideal
in our case because we'd like to use the same port numbers whenever
possible; that avoids piling up crap inside iptables in the (hopefully
unlikely) event that we die without cleaning up correctly.

Doing it in python instead of shell makes the code a bit less error prone.
Plus we can parse the iptables output and avoid triggering iptables errors.

When regenerating outgoing connections, we set TTL=42 to prevent re-proxying
of requests.  That's a little hacky, but at least it avoids infinite loops.

Importing options.py, ssh.py, and LICENSE from the bup project.