One of the great, rare joys of going to the movies is the delightful sensation of being surprised, even once but sometimes several times, by the changes in direction a story takes. Such is the case with the mind-blowing documentary “Searching for Sugar Man.” It’s best to enter as I did, knowing little or nothing about a shy, mysterious, black-clad singer named Rodriguez, who released two albums in the early 1970s that garnered favorable comparisons to Bob Dylan, then disappeared from the world.
