bug#13226: 24.3.50; set-file-acl on MS Windows shall check ACL string format

[Stefan Monnier]

> I think we are taking this feature out of proportions.  It was
> supposed to allow copying extended attributes from file to file; for
> that, we don't need to care whether the ACL is trivial or not.  But
> now we seem to start down the road of trying to interpret the ACL,
> which would need much more complex machinery.

That makes sense, yes.  BTW, I don't think we should document that
file-acl returns a string.  The representation should be documented
as undocumented and prone to change (ideally opaque).


        Stefan