It's been a rough month or so for Palm, as the only thing keeping the company's tanking stock price from falling completely into the gutter are buyout rumors -- RIM here, HTC there, even Lenovo, for some crazy reason. But that's apparently not enough to get CEO Jon Rubinstein down: he just sat down with Fortune for a remarkably candid chat, saying that although his company hasn't done so well, he still thinks there's potential -- and that he obviously wishes some things had gone better. The big one? The Verizon launch -- and Jon thinks that if the Droid and Pre had had their launch dates flipped, the Pre would have