Consume and return one command argument, stopping when it hits a character (not in a quotation) in `until`.

def cmdvalu(self, until=cmdquote):
        '''
        Consume and return one command argument, stopping when it hits a character (not in a quotation) in `until`.
        '''
        self.ignore(whitespace)
        if self.nextstr('"'):
            return self.quoted()
        if self.nextstr("'"):
            return self.singlequoted()
        return self.noms(until=until)