For some, Black Friday is the marker for the holiday season. For others, it’s the purchase of a Christmas tree. For many, to judge by the size and enthusiastic response of the audiences for last weekend’s Sierra Master Chorale Holiday Concerts, it’s the celebration of the musical traditions of the holiday. Sierra Master Chorale, entering its fifth season, delighted full houses with a program that acknowledged tradition yet offered new perspectives. SMC conductor Ken Hardin likes to challenge the 70-voice chorus and his audience with a variety of styles, periods and sentiments. He programmed a capella numbers, which put the …