git-sh-setup.sh:cd_to_toplevel problematic with symlinks

cd_to_toplevel takes the output of git rev-parse --show-cdup and feeds
it to cd.  The problem is that cd uses PWD to do what the user means
when saying cd .., i.e. it goes to /foo when in /foo/bar even though
/foo/bar might be a symlink.  Example:

    (in an existing git repository)
    /tmp/foo$ mkdir -p a/b
    /tmp/foo$ ln -s a/b c
    /tmp/foo$ cd c
    /tmp/foo/c$ git fetch . master:master
    git-fetch: line 108: /FETCH_HEAD: Permission denied

Is there any way to tell cd to ignore $PWD?

Another option is to have a new option to rev-parse which shows the
absolute path to tho toplevel.