Return a list of rulefiles for the given account.

        Returns an empty list if none specified.

def rulefiles(self, acc=None):
        """Return a list of rulefiles for the given account.

        Returns an empty list if none specified.
        """
        rulesdir = self.rulesdir(acc)
        rules = [os.path.join(rulesdir, x) for x in self.get('rules', acc, [])]
        if acc is not None:
            rules += self.rulefiles(acc=None)
        return rules