Behind a temporary wall and a beefy security guard warding off interlopers, slot machine manufacturer WMS Gaming showed off one of its most elaborate prototypes at the casino industry’s premier trade show last month — a slot machine based on the “Lord of the Rings” movie trilogy. It is complete with spinning symbols of goblets and swords, a digital Gollum who moans “precious” and a screen resembling an ancient map of a world inhabited by wizards, elves and, of course, hobbits.