[m-rev.] diff: revise progress message code

[Zoltan Somogyi]

This should not need review.

Zoltan.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Log.msg
Type: application/octet-stream
Size: 1693 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20211219/fd9725e9/attachment-0002.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DIFF.msg
Type: application/octet-stream
Size: 34865 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20211219/fd9725e9/attachment-0003.obj>