If you thought you knew the story of "The Princess and the Pea," the current Purchase Players production could turn your impression on its ear. This weekend, the Mayfield-based playhouse opened "Once Upon a Mattress." The original off-Broadway production starred Carol Burnett as the princess. Jacque Day spoke with the young director-music director team Samantha Doran and Justus Wright, about their collaboration on this play and others.