Comment 3 for bug 538024

This requires a model change. There are two proposals:
  * Edwin proposed that we store the distroseries that was checked.
    * We recheck each series.
    * This means we ask when a new series is started, but we know that
      new series are identical to the last series
  * Curtis proposed that we store the date when the answer was no.
    * We recheck every year -- allowing enough time for the series to diverge.