Improve debuggability in case of a stale LockFile

[league]

As noted in the comment on the LockFile constructor, it quietly busy-waits if a stale lock file is left behind after abnormal exit.

Should be relatively easy just to emit a message after a few seconds of busy waiting (Greg's suggestion).

In addition, if we store the PID (+hostname?) as suggested in the comment, then there is more information available for troubleshooting.

Issue pointed out as part of this ng-dp issue.

[dentalfloss1]

I'm working on this a bit since it is affecting some of my code

[dentalfloss1]

I should have looked at this more carefully, I see @league has already made some progress

[league]

@dentalfloss1 Thanks, it's okay. I saw something from you on Slack involving chrono, did you delete that branch?

I think my solution works and will help, but we can compare notes. The only question I have is whether this type of message on cerr would have been useful in figuring out that the "stuck" behavior is due to a leftover lock file. (We likely wouldn't have cerr redirected somewhere less visible, right?) I'll make a PR for visibility.