(Reuters) – Pop star Madonna urged Americans to support President Barack Obama during her concert in Washington D.C. on Monday night but incorrectly referred to him as a Muslim in her comments. In a video posted on YouTube by audience members at the concert, the singer delivers a rousing, profanity-laced political speech on freedom during her show. "Now, it's so amazing and incredible to think that we have an African-American in the White House … we have a black Muslim in the White House … …