If for nothing else, “The Best Exotic Marigold Hotel” deserves praise for courting an underserved box-office demographic (so-called “senior citizens”) and for assembling an energetic, wily A-team of E. Movies that celebrate the wisdom and ingenuity of senior citizens without condescension and ridicule are rare as pink giraffes. This is just one of the reasons I am so enthusiastic about The Best Exot. When it comes to unexpected sequels, a…