DALLAS — Davis Bertans hit a go-ahead 3-pointer with 1:41 left, and the San Antonio Spurs rallied from a 19-point first-half deficit to beat the Dallas Mavericks 105-101 on Wednesday night. The Spurs blew a six-point lead in the final period, but Bertans made his third 3-pointer of the quarter for a 99-96 lead and