parti.NNNN.log, where NNNN is the SZGClient ProcessID.
Maybe this too should be changed -- should we just try to log
to one big file, to limit clutter?  Every line is already labelled with [PID] now.

Don't use exit(0) in command parser.  Set a shared quit flag instead,
and have everybody (?) exit later.

<string>.append( C_string, len ) never copies in the string's trailing \000,
so add it ourselves.

Only create a listenSocket if we're the master -- avoid races to grab the port.
I'm not sure when is best to determine master-hood, so out of superstition
we do it in the first preExchange callback.

Yes, we *do* need to initialize cmdbuf_ to be *empty*.