There’s no overstating just how much Peter, Paul & Mary contributed to the commercial clout of folk music in the ‘60s, whether smoothing out the crags in several Bob Dylan songs, making squirrelly pop tunes out of Pete Seeger (“If I Had a Hammer”) and Woody Guthrie (“This Land Is Your Land”) compositions, or playfully bridging the psychedelic and kid-friendly (“Puff, the Magic Dragon”). But despite their friendly, nonconfrontational image, the trio also delivered stunning protest songs in “Cruel War” and “The Great Mandella (The Wheel of Life).”