inital work.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-tajo into TAJO-212
When two or more cast expressions are used, it will fail.
Completed.
Removed unused imports.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-tajo into TAJO-212
Merge branch 'TAJO-212' of github.com:hyunsik/incubator-tajo into TAJO-211