PACKEDBy 1990, the Pretenders had logged over a decade of touring and quite a few pop crossover hits. Certainly the band's sound matured, and there's a definite low key veneer to the foursome's fifth release. PACKED! is heavy on the melodic ballads, but then few imbue a simple mellow rocker with the passion of Chrissy Hynde, and as a group who's seen its share of true tragedy, the songs never ring insincere in the slightest. Opening single (and modern rock