Libevent's periodic timers aren't the right solution when the
timeout potentially changes every time.

This patch is designed to look good when you see it through 'diff -b':
it mostly leaves entries in the same order, and leaves the code unmodified.

Kevin Butler authored Nov 02, 2015 and Nick Mathewson committed Nov 13, 2015

(This is from Kevin's bug3199 patch series; nick extracted it into
 a new file and changed the interface a little, then did some API
 tweaks on it.)

Not good markdown, mind you.