The following contains MAJOR spoilers for the movie, “Serenity.”Sadly, I think we can all agree on one thing: There will be no grand parade of sequels to Joss Whedon’s “Serenity.”How much a few weeks (and a really poor box-office showing) changes things. Just a month ago, just before the film’s opening, fandom was abuzz with the hope and belief that Whedon’s against-all-odds comeback story would open big, launching what would become the next great science fiction franchise.After all, Whedon had rescued his beloved-but-all-too-short “Firefly” TV series from cancellation hell and brought it back as “Serenity,” a major motion picture. If he could do that, all things were possible, right?That was then.Now we fans have no choice but to watch the slow death of the “Firefly”/”Serenity” ‘verse on a …