Return list of volumes or diffs in this Store's selected directory.

def listContents(self):
        """ Return list of volumes or diffs in this Store's selected directory. """
        items = list(self.extraKeys.items())
        items.sort(key=lambda t: t[1])

        (count, size) = (0, 0)

        for (diff, path) in items:
            if path.startswith("/"):
                continue
            yield str(diff)
            count += 1
            size += diff.size

        yield "TOTAL: %d diffs %s" % (count, humanize(size))