Break out the AmEx black card – Barney’s Co-Op has moved in. Barney’s Co-Op yesterday opened at 3040 M St. NW, welcoming fashion conscious shoppers with discerning taste and deep pockets. The Co-Op’s M Street location was the temporary home of the Ralph Lauren store before it moved into its new digs on Wisconsin Avenue, and it has since been transformed into a modern space with a loft-like atmosphere. On previous trips to high-end stores,…