added more comments about FutureTask, Future and Runnable
added more javadocs for two main datastructure
added more javadocs for two main data structures
Merge branch 'master' of https://github.com/hluu/azkaban2
rebased to master
Merge pull request #281 from hluu/master

flowRunnerManager JMX bean : the NumExecutingFlows and RunningFlows values are not correct