'Return a comparison of actual and expected hash values.
Example::
Expected sha256 abcdeabcdeabcdeabcdeabcdeabcdeabcdeabcdeabcde
or 123451234512345123451234512345123451234512345
Got        bcdefbcdefbcdefbcdefbcdefbcdefbcdefbcdefbcdef'

def _hash_comparison(self):

    def hash_then_or(hash_name):
        return chain([hash_name], repeat('                or'))
    lines = []
    for (hash_name, expecteds) in iteritems(self.allowed):
        prefix = hash_then_or(hash_name)
        lines.extend((('                                Expected    %s    %s' % (next(prefix), e)) for e in expecteds))
        lines.append(('                                                    Got                                %s\n' % self.gots[hash_name].hexdigest()))
        prefix = '                or'
    return '\n'.join(lines)
