Bug 822882 - Additional timezone fixes relating to NOW()

The previous commit did not go far enough.  Specifically, all uses of NOW()
turned out to be suspect and needing to be fixed where it dealt with accuracy
ranges or talking with the server.  This also entailed fixing makeDaysAgo to
take the timezone offset, plus makeDaysBefore for when the date is null and
it ends up calling makeDaysAgo.

It was particularly important to calculate our effective end TS with the
timezone offset for our bisection calculation.  Otherwise, we ended up with the
same bisection loop on 2 days.

The other change is that when growing in the FUTUREWARDS direction, we also
want to observe the highest legal endTS there too.  We only differ in how we
calculate the initial endTS, but we still don't want to name a date that's
still in the relative future as our accuracy range, by definition, can't
include it.