Designers are human too. And most can't help showing a preference for long or short, full or slim in collections they show each season. For spring, however, even the most idiosyncratic designers straddle the fence in terms of length and width. They show short and long, full and slim--all in the same collection. The only consensus seems to be that everything is gently curvy. Bodices shape to the body. Waistlines are marked with belts or insets. Hiplines are emphasized, often by skirts that puff out beneath elongated torsos. And it's all accomplished with a grace and ease ideal for California living. In this sampling from some of the best-known fashion names, shape is definitely the thing for spring.