Sting's current ''Back to Bass'' tour is a tightly packed retrospective, assembling all the facets of his 36-year career into a neat two hours of the obvious hits, some international detours, and requisite ballads. The Ravinia show, the first of two consecutive sold-out nights, accommodated the expectations of anyone who entered the Sting camp early, middle, or late. He didn't push things much beyond those boundaries; instead, Sting performed with the consummate class of a professional who appears more relaxed in presenting his long line of musical trophies than he is earning any more for the shelf...