TAJO-989: Cleanup of child blocks after parent execution block is complete. (jinho)

Closes #103
TAJO-949: PullServer does not release files, when a channel throws an internal exception. (jinho)

Closes #76
TAJO-990: Implement a tool to find tajo configurations. (jaehwa)
TAJO-996: Sometimes, scheduleFetchesByEvenDistributedVolumes loses some FetchImpls.

Closes #109
TAJO-994: 'count(distinct x)' function counts first null value.

Closes #106
TAJO-999: SequenceFile key class need to be compatible. (jaehwa)

Closes #110
TAJO-928: Session variables should override query configs in TajoConf.

Closes #98
TAJO-947: ColPartitionStoreExec can cause URISyntaxException due to special characters. (Mai Hai Thanh via hyunsik)
TAJO-995: HiveMetaStoreClient wrapper should retry the connection. (jinho)

Closes #108
TAJO-1001: Add missed postgresql license to NOTICE.txt and LICENSE.txt.

Closes #114
TAJO-895: ConstEval should not be included in target list of projectable nodes.

Closes #111
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-991

Conflicts:
	tajo-yarn-pullserver/src/main/java/org/apache/tajo/pullserver/TajoPullServerService.java