leader election recipe sample code - dispatchEvent invocations can get out of order

Since the process method is not synchronized in org.apache.zookeeper.recipes.election.LeaderElectionSupport, therefore there is a race condition where events coming in from the watch may overtake the events dispatched during the start method.

A solution to ensure that events dispatched during the start method are handled before any watch-based events is to make the process method synchronized.