def history_file(self, location=None):
        """Return history file location.
        """
        if location:
            # Hardcoded location passed from the config file.
            if os.path.exists(location):
                return location
            else:
                logger.warn("The specified history file %s doesn't exist",
                            location)
        filenames = []
        for base in ['CHANGES', 'HISTORY', 'CHANGELOG']:
            filenames.append(base)
            for extension in ['rst', 'txt', 'markdown']:
                filenames.append('.'.join([base, extension]))
        history = self.filefind(filenames)
        if history:
            return history
Return history file location.