ZOOKEEPER-1382. Zookeeper server holds onto dead/expired session ids in the watch data structures
  (Germán Blanco and Michael Morello via camille)

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/branches/branch-3.4@1550220 13f79535-47bb-0310-9956-ffa450edef68