With this change,
pkill -SIGUSR1 -f runtornado
will dump the stack and SIGUSR2 will enable an interactive debugging
session.
This fixes#613 for Tornado which was the original motive for that
ticket; I'm not sure whether we want to do this for our Django
processes as well, but it would be easy to do so if we did.
(imported from commit a7de7c6070f4bf0404bed6f434e6a6b291d66a26)
Tim Abbott