Don't lock the handshake queue

There's no reason (I can currently think of) that listeners cannot
"listen" on the same queue.
Be explicit about using acks though.
Ignore my scratch notes
Rename queue argument to service

I'm about to add options that also mention a queue, and I don't want
confusion.
Ops. Make sure I keep up with my own changes.
Implement --send and --recv

These relay to a queue from stdin or to stdout from a queue, but just
the one way, i.e., without the connection stuff.