Strangers to success, the new Boston Celtics see their perfect record as something to improve on. Their 91-69 victory over the New Jersey Nets on Wednesday night gave them their best start in 35 years, but coach Doc Rivers gave another number to their 7-0 record. “Means zero, really,” he said. Early in the season, the Celtics are focusing on their flaws and not the uptempo game and shutdown defense…