Clarify notice if no file-specific diff caused fallback. (MR: !19)

                        if self.magic_file_type != 'data' else ''

                    difference.add_comment(

                        "Format-specific differences are supported for this "

                        "file format but none were detected{}".format(suffix))

                        "file format, but no file-specific differences were "

                        "detected. Falling back to a binary diff.{}".format(suffix))

            except subprocess.CalledProcessError as e:

                difference = self.compare_bytes(other, source=source)

                if e.output: