This will eventually allow us to use analytic derivatives instead
of finite differences.

The current algorithm is not very robust and is sometimes
catastrophically slow.  However, it's able to fit much more general
models than the HSC-side one we'll be adding shortly, so we'd like to
keep it around.

This task is slated for eventual removal, but that's more work than we
want to do on this ticket.  For now, we just need to remove a name
collision.

Many of these passed on my Ubuntu box, but not
on CentOS CI.