DCist had a very tough choice to make last night. We were definitely going to a concert, but which one? Icelandic mood rockers Sigur Ros in Baltimore? Sweet singing Canadian chanteuse Feist at the Birchmere? Scottish indie rockers Idlewild at the Black Cat? We were in quite the predicament so we had to check our concert going guidelines which clearly state, whenever in doubt, go see the band with the Scottish accent. So Idlewild it…