The crowd was spilling out of Detroit’s, The Majestic to see a sound line-up for Mustard Plug’s Holiday Show on December 29, 2011: Flatfoot 56 The Parka Kings Mustard Plug The Suicide Machines If Flogging Molly and The Tossers had a baby, Flatfoot 56, a Celtic punk rock bank from Chicago, would probably be their son. They were a solid opener and had no trouble getting people to dance. Flatfoot 56 amped the crowd up with their rapid, energetic music: a piercing bagpipe, a fury of drums, a driving bass, a harmonious mandolin, and a fast-paced guitarist with a gruff, Irish tinted voice. They played songs like, “Chinatown Jail Break,” and…