Use a bigger buffer for most write-an-SFS-to-a-file jobs.
Only write the bookmarks file if we actually updated the edition. It is possible, especially on startup, to get callbacks that don't increase our edition number.
Save bookmarks lazily on edition updates - wait 5 minutes to hopefully bundle a bunch of changes together, and ensure we don't write them more often than every 5 minutes.
Guarantee that node-throttle.dat and client-throttle.dat always get written on shutdown.
Fix synchronization problem in shutdown hook.
Move period to constant
Increase persistence interval from 1 minute to 15 minutes for node-throttle.dat, client-throttle.dat