[m-rev.] for possible post-commit review: move .used file parsing to used_file.m

[Zoltan Somogyi]

Most of this just moves code, but some of the moved code
was also modified.

Zoltan.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Log.recomp7
Type: application/octet-stream
Size: 980 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20210829/ce5b5e1b/attachment-0002.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DIFF.recomp7
Type: application/octet-stream
Size: 80259 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20210829/ce5b5e1b/attachment-0003.obj>