A week shortened by the Memorial Day holiday produced a session filled with gratuitous price swings that left the broad averages largely unchanged. Even so, shorts were caught in the ringer at the closing bell, suggesting it’s possible the S&Ps will trade at a new all-time high in the early going Thursday. If they end the day in record territory, bears had better dive for cover ahead of the weekend.  Fridays have not lived up to their reputation for freakiness in recent months, but this one could be an exception.