[MLton] mlbs and soft and hard links

[Matthew Fluet]

> z.mlb:
>   a/a.mlb
>   b/b.mlb
> a/a.mlb:
>   $(MLTON_ROOT)/basis/basis.mlb
>   a.sml
> a/a.sml
>   print "a\n";
> b/b.mlb: --> a/a.mlb  (hard link)
> b/b.sml:
>   print "b\n";

I think you meant to have

b/a.sml:
  print "b\n";

> I guess what I am saying is that the correct unit of caching for mlb
> files in the elaborator is *not* OS.FileSys.file_id, but rather
> absolute path.  I don't see any reason to complicate the semantics
> with notions from the underlying file system.

That's fine with me.