Lindsey Buckingham has released only four albums as a solo artist in 25 years. While he remains active as a producer and session musician, this is his first offering in 14 years. Those who saw Cameron Crowe's film Elisabethtown got a sneak peak: Buckingham's "Shut Us Down" was featured in the film. Under the Skin is perhaps the most nakedly visible and tender recording he's ever dropped. He wrote much of the set while on tour with Fleetwood Mac in 2003…