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 JavaByteCode
added timestamp, date, and time variables.
Refactored method visitor.