Use cliTable for printing help in the CLI.
Discare pure acks from the inbox.

With this change, pure ack messages (those with an empty Body) will be
discarded after processing and no longer kept in the inbox.
Ensure that go failures don't leak server processes.

It was previously possible, if one hit a panic in a test, to have server
processes hanging around afterwards.

This change installs a lifeline file descriptor in the server process so
that, when the kernel cleanup up the test process, the server will see
EOF and can exit.