Unlike the music of Christmas or Easter, the music of Thanksgiving is harder to pinpoint.  Shuffling leaves?  The drum-brush strokes of a knife carving the turkey?  Vince Guaraldi, an early lead-up to Christmas through the dim or vivid Charlie Brown television-memories of readers of a certain age?  An uncertain business, but here are a couple of thoughts. First, when in doubt, start in the seventeenth century.  The “Te Deum & Jubilate for Voices and Instruments made for St. Cecilia’s Day 1694” of Henry Purcell was apparently performed as a Thanksgiving piece, as noted by Michael Evans Kinney and the Stanford libraries: While not much is known about the early St.…