fix exported vertex normals (on Blender 2.49)

While surface normals show vertical to face correctly in 3D view, the blender .obj exporter sometimes uses another normal data. The normal data seem to not surface normals but vertex normals.

To fix them, in 3D view select the face exported with unwilling normal data and run command Mesh > Faces > Set solid. After setting faces solid, the exporter would not use vertex normals.