update hadoop dependency to 2.4.0
Merge remote-tracking branch 'origin' into yingdac_updatehadoop_846
A test for Exceptions thrown by Threads spawned by Task.call()

This PR adds a test of the exception handling when a Thread spawned by `Task.call()` throws a Exception. The test passes if that thriggers a `FailedTask` in the Driver that contains the thrown Exception as the (ultimate) cause.

This test invalidates the hypothesis for #908, as it currently passes.
Merge pull request #914 from Microsoft-CISL/weimer_rogueThreadTest

A test for Exceptions thrown by Threads spawned by Task.call()
remove unused line in testGetEvaluatorList
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
Closing #930: Add Idempotent annotation.

Also updating the license headers.
Closing #932: A .toString for JobMessage
Merge pull request #939 from Microsoft-CISL/weimer_930

Closing #930: Add Idempotent annotation.
Merge pull request #940 from Microsoft-CISL/weimer_932

Closing #932: A .toString for JobMessage
Merge pull request #847 from Microsoft-CISL/yingdac_updatehadoop_846

update hadoop dependency to 2.4.0
add a recovery flag to proto to indicates communications from orphan evaluators for recovery
minor format change and bug fixing
remove unnecessary hasRecovery check
undo mutable evaluatorId change