TAJO-762: Implements current date/time function (Hyoungjun Kim via hyunsik)

Closes #16
TAJO-853: Refactoring FilterPushDown for OUTER JOIN
If catalog runs with HCatalog, partition column is a qualified name
Else partition column is a simple name
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-853

Conflicts:
	tajo-client/src/main/java/org/apache/tajo/client/TajoClient.java