Of the available green heroes, the Incredible Hulk, Kermit the Frog or even Al Gore seems more likely to carry a movie than Green Lantern. But the third-string DC Comics character has nonetheless been selected to hold the super-being turf at the world’s megaplexes for a few weeks, between “X-Men: First Class” and “Captain America: The First Avenger.” “Green Lantern” is capable of doing that, although it’s neither amusing nor exciting enough to ensure a long-running franchise. Like Captain America, Green Lantern is a “Golden Age” comics hero, debuting in 1940 — a simpler time for strong-jawed do-gooders.