Fix :func:`shutil.copymode` and :func:`shutil.copystat` on Windows.
Previously they worked differenly if *dst* is a symbolic link:
they modified the permission bits of *dst* itself
rather than the file it points to if *follow_symlinks* is true or *src* is
not a symbolic link, and did not modify the permission bits if
*follow_symlinks* is false and *src* is a symbolic link.