set rally point altitude(s)

def set_alt(self, i, alt, break_alt=None, change_time=True):
        '''set rally point altitude(s)'''
        if i < 1 or i > self.rally_count():
            print("Inavlid rally point number %u" % i)
            return
        self.rally_points[i-1].alt = int(alt)
        if (break_alt != None):
            self.rally_points[i-1].break_alt = break_alt
        if change_time:
            self.last_change = time.time()