By Sara Morrison LOS ANGELES (TheWrap.com) – Dr. Martin Luther King, Jr.'s historic "I have a dream" speech turns 50 on Wednesday. Its anniversary will be celebrated in Washington D.C., where it originally occurred, with speeches by Presidents Clinton, Carter and Obama. Members of King's family and civil rights leaders will also be in attendance. Obama's speech will be delivered at the Lincoln memorial – from the same spot as King's – at is set to begin at 2:45 p.m. ET. …