Spiderland, the second and final full-length album by Louisville, Kentucky post-rockers Slint, is getting expanded in a big way this spring with a multi-disc box set. Considered to be one of the best records of its subgenre, brimming with shifting dynamics and intense, narrative lyrics (rumors circulated that the brief, tense sessions that birthed the record sent at least one of the band’s members into a psychiatric hospital for a stay), Spiderland was nonetheless ignored by many upon first release, save a pivotal appearance of closing track “Good Morning, Captain” on the soundtrack to…