+ children
+
+ We assume that the children the refpoints of the children are still
+ found at 0.0 -- we will fuck up with thresholds if children's
+ extents are already moved to locations such as (-16, -8), since the
+ dy needed to put things in a row doesn't relate to the distances
+ between original refpoints.
+
+ TODO: maybe we should rethink and throw out thresholding altogether.
+ The original function has been taken over by
+ align_to_fixed_distance().
+*/