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
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-774_2
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
Fixed travi-ci message problem.
TAJO-867: OUTER JOIN with empty result subquery produces a wrong result. (Hyoungjun Kim via hyunsik)
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-867
TAJO-867: OUTER JOIN with empty result subquery produces a wrong result. (missed github issue close.)

Closes #35
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-774_2

Conflicts:
	tajo-core/src/main/java/org/apache/tajo/engine/planner/ExprNormalizer.java
Moved test queries to sql files.