bug#6995: 24.0.50; get-free-disk-space doesn't return available space in dired

[Chong Yidong]

Glenn Morris <rgm@gnu.org> writes:

> Because the filesystem name is long, the numerical values do not line
> up with the column headings. The current code seems to assume that
> they do line up. Thus, running dired on "~" gets wrong values for the
> total size.

I've just checked in a change to use the "%" as an anchor for finding
the available space, instead of assuming the columns line up.  Patches
to avoid using `df' welcome...