Convert normal from object to world space

Properly doing this is a bit more complicated because it has to be normalized and pointing in the right direction. Just applying the inverse of the transform matrix doesn't quite do it.

src/object.cc

@@ -88,7 +88,8 @@ Vector4
 Object::Normal(const Vector4& p)
     const
 {
-    return FromObjectSpace(DoNormal(ToObjectSpace(p)));
+    Vector4 norm = Transpose(mTranslation) * DoNormal(ToObjectSpace(p));
+    return norm;
 }