fix and test sync growth into the future

- Our use of FUTURE() in time-warped tests was hurting our test coverage,
  specifically as it related to us using NOW() for our sync range boundaries
  (which is not quantized!) whereas FUTURE() was quantized.  I have removed
  FUTURE() entirely.  The main rationale for its presence was for cases like
  the INBOX where we wouldn't want our test to be affected by new messages
  showing up.  Since we really want our tests to happen in folders we
  completely control or we really want the INBOX and its weird semantics, this
  was not helping.

- Fix bugs related to NOW() and being quantized.  Our range-shrinking logic was
  getting faked out by rounding us into the future for refreshes and has been
  corrected.

- syncedEntireFolder has been changed to syncedToDawnOfTime since that is a
  more accurate statement since we no longer are expecting to have the
  invariant that we have synchronized everything from the front-to-the-back.
  (Currently the invariant roughly holds, but this will stop being true when
  we start synchronizing less than a day and have refresh in its overflow case
  also be more willing to give up and not refresh everything that was asked of
  it.)

- Stopped us from trying to synchronize into the deep future just like we used
  to try and synchronize into the deep past.