Oops . . . CBS did it again. First, cybersleuths carefully deciphering the network’s Web site believe they found a dead giveaway of which “Survivor” will pick up the Aug. 23 $1 million grand prize (the supposed winner wasn’t blotted out with a red “X”). Yesterday, the evening’s edition of the No. 1-rated show was spoiled by an early posting that described the outcome of the show, six hours before broadcast. Richard Foster, a writer in Richmond, Va., told the Associated Press that he was checking the site on Wednesday afternoon only to be startled when he saw a headline — linked to the full story — that revealed which of the nine remaining island inhabitants would get the boot on that night’s episode. Foster then posted the revelation on the local news site he works for. Greg Buis, the practical joker from Colorado, was last night’s victim — according to both Foster and the show.