ENH:In vtkDataSet, fixed the logic of the scalar range computation to match the one of the bounding box computation (added ComputeScalarRange and ScalarRangeComputeTime).
BUG:In vtkUniformGrid, fixed scalar range computation. It was always performing the computation without caching the result.
ENH:In vtkHierarchicalBoxDataSet, added GetScalarRange, ComputeScalarRange and ScalarRangeComputeTime.