Serving up more highlights from the vast, brash cartoon canon that made the first volume of Looney Tunes a surprise laserdisc best-seller, Vol. 2 might look, from its nearly identical packaging, like sloppy seconds. In fact, it’s a thoroughly fresh, new meal. Each hour-long disc side forms a themed ‘toon treatise on some Warner-short trademark, be it a genre style or an ingeniously strip-mined stock story line (the final program rounds up seven sleepless-night scenarios). More than half of the 70 cartoons aren’t available on tape, so disc sides devoted to star Warner directors like Chuck Jones resurrect lots of seldom-seen delights. While a few of these finds, like Jones’ ”The Little Lion Hunter,” are built around the sort of painful shuffling-Negro caricatures so common in ’40s Hollywood, most showcase a barbed, MTV-paced visual wit that hasn’t dated a bit. Don’t let that be all, you folks at MGM/UA — bring on Vol. 3.