BOOKKEEPER-662: Major GC should kick in immediately if remaining space reaches a warning threshold (sijie via ivank)

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/bookkeeper/trunk@1558410 13f79535-47bb-0310-9956-ffa450edef68
BOOKKEEPER-710: OpenLedgerNoRecovery should watch ensemble change. (sijie via ivank)

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/bookkeeper/trunk@1559192 13f79535-47bb-0310-9956-ffa450edef68
BOOKKEEPER-429: Provide separate read and write threads in the bookkeeper server (Aniruddha via sijie)

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/bookkeeper/trunk@1559917 13f79535-47bb-0310-9956-ffa450edef68
BOOKKEEPER-696: stats collection on bookkeeper client (Aniruddha, ivank via sijie)

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/bookkeeper/trunk@1559918 13f79535-47bb-0310-9956-ffa450edef68