New extension: pass ln, for symlinks

[Radon Rosborough]

> See patch attached

Thanks for sharing - I do think this would be better implemented as an
upstream patch, but I asked previously if such a patch would be
merged, and received no confirmation on this for about a month, which
is why I proceeded with an external plugin.

If one of the maintainers does decide to merge this, I might advise
first looking at my work as well, since it handles some edge cases
that should be considered, particularly with regard to distinguishing
between file and directory links.