Figure out if time offsets between servers in a cluster cause issues with the log's integrity

[mreithub]

Since we're using timestamps to identify changes (and to tell when each log record was active), having a time offset on two servers in a database cluster might be a problem (if now() simply reports the system time on each server).

I haven't actually dealt with PostgreSQL clusters yet though (plus there seem to be different implementations), so it's entirely possible this won't be an issue