[m-rev.] for post-commit review: implement PROPOSED searches for .a, .init, .jar and .dll files

[Peter Wang]

On Wed, 27 Nov 2024 20:30:41 +1100 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> This completes the initial draft of the code for
> searches in the PROPOSED install library structure.
> For review by anyone. I am particularly seeking feedback
> on the updated error messages in handle_options.m.

mmc --output-libgrades produces no output after this change
(commit 8f4aeaf02).

In detect_stdlib_grades, chosen_stdlib_dir is (still) set to `no'.

Peter