code I found in /foo/x/mike/src/capture/capture.c. Second, add a -r
option to open up a second log file called the "run" file, which is
intended to be used for the experiment session log. This log is
restarted with a SIGUSR1. Third, add SIGUSR2 handler to close the
pty side of the capture, which has the nice side effect of causing tip
to exit gracefully.