TAJO-1037: KillQuery hang in subquery init state. (jinho)

Closes #137
TAJO-1015: Add executionblock event in worker. (jinho)

Closes #124
Fixed many bugs.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into EliminateDatum

Conflicts:
	tajo-core/src/main/java/org/apache/tajo/master/TajoContainerProxy.java
	tajo-core/src/main/java/org/apache/tajo/worker/TajoWorker.java
	tajo-core/src/main/java/org/apache/tajo/worker/Task.java