[m-rev.] for post-commit review: add_costs

[Peter Wang]

On Fri, 16 Oct 2020 07:26:29 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> For review by anyone.
> 
> Zoltan.

> Clarify the code of add_goal_costs_seq.
> 
> And add documentation and an XXX.

That looks fine, in that the behaviour looks to be unchanged.

Peter