update hadoop dependency to 2.4.0
Merge remote-tracking branch 'origin' into yingdac_updatehadoop_846
Move REEFFileNames ahead of HADOOP classpath entries
Merge pull request #920 from dafrista/bcho_change_yarn_classpath

Move REEFFileNames ahead of HADOOP classpath entries
netty4 only changes (w/o MLSS stuff)
minor refactoring in groupcomm operators
Merge remote-tracking branch 'origin' into yingdac_updatehadoop_846
use the KeepContainersAcrossApplicationAttempts=true for driver submission, so that we can keep evaluators running when driver crashes
Merge branch 'yingdac_updatehadoop_846' into reef-bridge
update driver to unsigned