GRACE POTTER She and her Nocturnals look a little more glam, but they’re grittier than ever   By Russell Hall  Back in 2010, fans of Grace Potter and the Nocturnals had a couple of big changes to deal with. First there were two new members, bass player Catherine Popper and guitarist Benny Yurco. But for listeners who had been following the band since it first hit the jam-band circuit in the early 2000s, the second change might have been even...