[m-rev.] for post-commit review: improve error messages for initialise/finalise

[Zoltan Somogyi]

For review by anyone.

Zoltan.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Log.if
Type: application/octet-stream
Size: 622 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20210524/9a8cdf93/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DIFF.if
Type: application/octet-stream
Size: 15034 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20210524/9a8cdf93/attachment-0001.obj>