WASHINGTON - Gay activists have a message for Vice President Cheney's gay daughter: Mary, Mary, be contrary. Mary Cheney, a former lesbian activist who heads the veep's reelection campaign, has been silent on the White House's proposal to ban gay marriage. Now, thousands of gays are sending her postcards via a Web site - DearMary.com - that hopes to bring the battle home to the White House. "Two years ago, this woman was the gay mascot of the Republican Party, wooing us for our money and our votes," said John Aravosis, who set up the Web site. "She sold us...