LOS ANGELES (Reuters) - Country pop darling Taylor Swift retained the top spot of the Billboard 200 album chart on Thursday after strong sales during the holiday season that saw her album "Red" mark its sixth week at No. 1 since its release two months ago. "Red" sold 275,000 copies last week ahead of the holidays, according to figures from Nielsen SoundScan. Swift, 23, was able to hold off rapper T.I.'s new album "Trouble Man: Heavy is the Head" from the top spot. The rapper came in at No. 2 after selling 178,000 copies. T.I. ...