[m-rev.] diff: stop using digraph.{tsort,atsort}

[Zoltan Somogyi]

This should not need review.

Zoltan.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Log.dg
Type: application/octet-stream
Size: 1216 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20230622/62679d73/attachment-0002.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DIFF.dg
Type: application/octet-stream
Size: 15294 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20230622/62679d73/attachment-0003.obj>