Do politics belong in music? They sure do, especially when delivered as entertainingly as by this handful of radically independent singer-songwriters. Indie folk singer and activist Erin McKeown owes much to the topical songwriting of folk legend Tom Paxton. Bedazzled creature Taylor Mac and band perform selections of political songs from his upcoming 24-hour concert of the history of popular music. Daniel Kahn, whose Painted Bird has been called “the Yiddish Pogues,” is to klezmer music what blues singer Pura Fé, founder of a cappella trio Ulali, is to Native American music.