SHANNON & THE CLAMS Onion (Warner) This is a kind of partner to the other album reviewed here today, by The James Hunter Six, whose album also bridges the 1950s and the 1960s from an across-the-Atlantic perspective to Shannon & The Clams. Americans Shannon Shaw and Cody Blanchard have a similarly long history to the English sextet, Onion being their fifth album. And as with the Brits, Shannon & The Clams play a kind of music that long ago went out of fashion but never really