You never know what Cassandra Wilson might sing. From album to album, she has shown bold originality, weaving a rich tapestry of music from jazz to folk, pop to blues. A recent sold-out concert at the Great American Music Hall in San Francisco proved that Wilson is still unconfined by musical boundaries. Barefoot and wearing a white dress, Wilson opened with Bob Dylan’s "Lay Lady Lay," wrapping her deep, rich voice around the line "Lay across my big brass bed." Her last CD, "Belly of th