Merle Haggard has recorded literally hundreds of albums and thousands of songs in his career, and at age 72 he shows no signs of slowing down. He's released 11 albums in the last decade — everything from an album of honky-tonk classics to duets with George Jones and a bluegrass disc recorded mostly live in the studio. Put on any of Haggard's 38 Number One songs and you'll immediately understand why he's one of the most important singers and songwriters in American pop music history. But...