B.B. King played coy at the 25th annual Chicago Blues Festival last weekend. “I won’t say what party I’m for,” the great vocalist and guitarist began, in obvious reference to local resident Barack Obama’s ascension to Democratic presidential nominee, “but everybody has something to be happy about now. Including the women — who found out ‘Yes, we can!‘” Few other of the hundreds of performers were even that explicit onstage, but the fest reportedly drew 750,000 listeners over four days, and the music projected a general air of triumph against daunting odds.