[PATCH 4 of 4 V2] obsolete: allow cycles

[Jun Wu]

Excerpts from Augie Fackler's message of 2017-03-23 20:59:03 -0400:
> > For clocks going backwards, we can detect that, say we get
> > maxdate = max(m.date for m in markers), then if we are going to write a
> > marker with date < maxdate, we could warn people, and/or write 
> > (date+rand(0 to 1)) as a fake date. That would at least make non-exchange
> > experience always expected.
> 
> Could we default to using the current timestamp, but if there’s a member
> of the obsmarker chain we’re about to add to with a time ahead of our
> clock, we do (that time + rand(0,1)) as the time? Greg, does that
> alleviate most of your concern around using times?

That was what I suggested. A warning is probably worthy if that happens.

More strictly, when loading the obsstore, if any marker has a time greater
than the local system time, it may be worth a warning so we can detect
problems early.

> (This has the negative that in the presence of marker cycles time is
> somewhat a lie, but I think the overall ergonomics seem to be about right
> at least as a thought experiment...)