It's been more than three years since the Dixie Chicks sparked a media firestorm by announcing they were "ashamed the President of the United States is from Texas." Now, the embattled country stars are reigniting the blaze with a highly controversial documentary featuring lead singer Natalie Maines calling President Bush a "dumb f---." According to Entertainment Weekly, one memorable scene from "Dixie Chicks: Shut Up and Sing" shows the singers watching a news report on President Bush's reaction to their infamous on-stage comment. In the report, Bush says ''the Dixie Chicks are free to speak their mind,'' adding, ''they shouldn't...