TAJO-978: RoundFloat8 should return Float8Datum type. (Hyoungjun Kim via hyunsik)

Closes #96
TAJO-979: Dividing float value by zero should throw "Divide by zero Exception" (Hyoungjun Kim via hyunsik)

Closes #100
TAJO-987: Hash shuffle should be balanced according to intermediate volumes.

Closes #101
TAJO-966: Range partition should support split of multiple characters.

Closes #91
TAJO-975: alias name which is the same to existing column name may cause NPE during PPD.

Closes #92
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
Merge branch 'master' of http://git-wip-us.apache.org/repos/asf/tajo into index_support

Conflicts:
	tajo-core/src/main/java/org/apache/tajo/master/GlobalEngine.java
	tajo-core/src/test/java/org/apache/tajo/engine/planner/physical/TestPhysicalPlanner.java