When the Norton Museum of Art asked the West Palm Beach city commission to overrule the city's historic preservation board and OK the destruction of a 1920s garage to make way for the museum's latest round of expansion, the trustees expected to get their way. Not in Mango Promenade. The residents of this narrow peninsula of a neighborhood, less than 12 blocks long and a block and a half wide, have watched the well-funded cultural Goliath grow and devour their district's northernmost blocks through the years. Not this time. Mango Promenade was the city's very first automobile suburb, said the working folk whose sweat equity had revived the neighborhood in recent years, and those old garages are central to its character. The Mangoistas took that argument to a packed city hall hearing in February, outdueled a team of Norton lawyers and architects, and convinced the commission, for once, to do the right thing.