change Monitor back to a Mutex for @start_stop_mutex
change Monitor back to a Mutex for @start_stop_mutex

rickypai/zookeeper,songling88/zookeeper,rickypai/zookeeper,zk-ruby/zookeeper,zk-ruby/zookeeper,rickypai/zookeeper,songling88/zookeeper,rickypai/zookeeper,songling88/zookeeper,songling88/zookeeper,zk-ruby/zookeeper