Kevin Keegan quit as Newcastle United manager for a second time following a dispute over player transfers, a day after Alan Curbishley resigned from English Premier League soccer rival West Ham for the same reason.Keegan, who also quit Newcastle in 1997, received a letter yesterday from managing director Derek Llambias that failed to resolve the issues, the League Managers Association said in a statement. Keegan held the job for less than eight months and said he had ``worked desperately'' to r