TAJO-757: Add parser rule and algebraic expression for window function. (hyunsik)
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into window_function

Conflicts:
	CHANGES.txt
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into window_function
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into window_function
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into window_function

Conflicts:
	CHANGES
	tajo-algebra/src/main/java/org/apache/tajo/algebra/Expr.java
 TAJO-880: NULL in CASE clause occurs Exception. (Hyoungjun Kim via hyunsik)

 Closes #40
TAJO-848: PreLogicalPlanVerifier::visitInsert need to find smaller expressions than target columns for a partitioned table. (jaehwa)
TAJO-879: Some data is missing in the case of BROADCAST JOIN and multi-column partition. (Hyoungjun Kim via jaehwa)
TAJO-850: OUTER JOIN does not properly handle a NULL. (Hyoungjun Kim via hyunsik)

Closes #22
TAJO-853: Refactoring FilterPushDown for OUTER JOIN. (Hyoungjun Kim via hyunsik)

Closes #28
TAJO-886: Add IRC page to community section in site.

Closes #45
TAJO-882: CLI hangs when a error occurs in the GlobalPlanner. (Hyoungjun Kim via hyunsik)

Closes #42
TAJO-887: Eliminate HiveQL support feature.

Closes #46
TAJO-887: Eliminate HiveQL support feature. (missed elimination of hiveql config).
TAJO-890: Redirect stdout of maven test to /dev/null in Travis CI script.

Closes #47
TAJO-866: COUNT DISTINCT with other aggregation function throws ClassCastException. (Hyoungjun Kim via hyunsik)

Closes #36
TAJO-874: Sometimes InvalidOperationException occurs when aggregates TableStat. (Hyoungjun Kim via hyunsik)
TAJO-874: Sometimes InvalidOperationException occurs when aggregates TableStat. (Hyoungjun Kim via hyunsik)

Closes #38
TAJO-884: complex join conditions should be supported in ON clause.

Closes #44
TAJO-881: JOIN with union query occurs NPE. (Hyoungjun Kim via hyunsik)

Closes #48