Make whats-in-port and clear-port agree on what is in a port

[purinkle]

bin/clear-port and bin/whats-in-port are a pair. Since #789 they no longer
agree on what "in the port" means.

$ grep lsof bin/clear-port
  lsof -ti4TCP:"$1" -sTCP:LISTEN | xargs -r kill

$ grep lsof bin/whats-in-port
  lsof -ni4TCP:"$1"

clear-port now looks only at the listening process. whats-in-port still
lists every socket on that port, so it includes established connections. A
browser with the page open shows up there.

The result is that whats-in-port 3000 can list processes that clear-port 3000 will not touch. Someone reads the first, runs the second, and the thing
they saw is still running.

#789 was right to narrow clear-port. Killing a browser because it had the
page open was the bug. The question is whether whats-in-port should narrow
to match.

Two ways to settle it:

• Add -sTCP:LISTEN to whats-in-port, so both answer the same question.
  Simple, and the pair stays honest.
• Leave it wide on purpose, because seeing every holder of a port is useful
  when you are working out what is going on. If we choose this, say so in a
  comment in both scripts, so the difference reads as deliberate.

Either is defensible. Having it happen by accident is not.