Another week, another folk tale hits movie theaters. Hot on the heels of the modestly performing “Hansel & Gretel: Witch Hunters” comes “Jack the Giant Slayer,” an attempt to expand the old English tale into a big budget epic. “Jack” comes with some giant-sized names attached, particularly Bryan Singer and Christopher McQuarrie (the directing and writing duo behind “The Usual Suspects”), but you’d never guess that from the shoddy production values and uneven tone.