You might think that Mason Jennings’ decision to become a member of Jack Johnson’s Brushfire label family would be an iffy move for the fiercely independent singer-songwriter that he is, and whether the association would soften his style. I did, until I saw him play at the Bluebird last Friday night. I was certain I would be subject to a too-clean, pop-folky string of bouncy, happy tunes, the ilk of which build up the majority of Johnson’s oeuvre. Not so. Jennings remains a strong, almost surly and unabashedly political songwriter, with more in common with Paul Westerberg or Elliott Smith than the lighthearted crooner.