A few minutes before nine yesterday morning, John Farrell walked through double doors in the Red Sox’ clubhouse, Dustin Pedroia nipping at his heels. They were grinning like third graders, still chuckling over what almost certainly was another wisecrack from the trash-talking second baseman. Snap a picture, scribble “Greetings from Fort Myers” across the top, and you’d have a postcard from Red Sox spring training. If Disney World is the happiest place on earth, Camp Farrell is a narrow runner-up. A few days ago, team president Larry Lucchino referred to “good vibrations” emanating from JetBlue Park, but not even the Beach Boys could do justice to the mood here. “Everyone’s positive,” Pedroia said, “and when you’re around people that are positive, you want to go out there and push yourself and do all you can do to not let them down.” Of course, none of this guarantees the Red Sox will have a winning season, especially after last year’s 93-loss debacle. None of this would be noteworthy, either, if not for the stark contrast to a year ago.