only malloc the data buffer for 'get' if necessary, also, zero it
only malloc the data buffer for 'get' if necessary, also, zero it

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