Wilco guitarist Nils Cline manages to show off his legit guitar chops at every opportunity without ever stretching the band’s credibility as a low-key Americana outfit. Cline’s a technician with an ear who fits seamlessly in a group that quotes country western, rhythm and blues, and southern rock. But when he’s not playing with the band that penned “Bull Black Nova”, he’s tooling around in the wilds of avant-jazz. For graduate-level Wilco fans and guitar…