specific to images is only called on images.  So this fixes a bug where the
image version of have_same_dimensions() was being called for tensors and
therefore only looking at the nr and nc dimension while ignoring the others.
This caused some parts of the DNN tooling to malfunction.

limit on pixel chain recursion depth.

python API.

so that things are a little more consistent.

instead of the bad old way that only really worked for square boxes.