RUSH Limbaugh put out a statement yesterday that he and his third wife, Marta, had separated — but only after PAGE SIX called to confirm what we'd learned exclusively. Sources in Palm Beach say Marta dumped the burly blowhard and vacated the couple's home on North Ocean Boulevard. The two are quietly working out a divorce agreement. Limbaugh met Marta on the Internet and they married in 1994. Since