“This Is Spinal Tap” By MANOHLA DARGIS Few movies take possession of you like “This Is Spinal Tap,” the delightful shaggy-haired 1984 rock-n-roll parody that turned Rob Reiner into a filmmaker. The movie, about a ridiculous group of heavy-metal rockers, didn’t set the world or entertainment industry on fire on its release. Yet it kick-started an unlikely career that rapidly picked up momentum with crowd pleasers that won love and sometimes awards, and often cleaned up at the box office....