VoltDB/voltdb — pull request #498 by rbetts (2013-05-03 21:14:05+00:00)
Title: ENG-4617 Catch SessionExpired in leader elector

It is possible that the leader elector callback runs on a dead session. A dead session is shutting down ZK. Don't crash on this exception. If the session is dead, a next viable leader
elector will run anyway.