This is the other way to allow ports to work when the processes
themselves cannot be enumerated: just report the port with an empty
description. We need to do some work to make sure this is safe for the
client; see comments.
- Reverse connections must be maintained to ensure messages are
processed in order. (Whoops!)
- The clipboard context must remain live in order for the data to
remain available for applications, at least on X11. (And it couldn't
hurt elsewhere, either, I guess.)
- Print out the server version at startup time, so we can be sure what
we're talking to.
- Print out the full details of the error when something goes wrong
with `browse` or `clip`.
