TAJO-1129: Remove hadoop 2.2.0 support. (jinho via hyunsik)

Closes #215
TAJO-1154: TajoCli doesn't pause while running the non-forwarded query. (Hyoungjun Kim via hyunsik)

Closes #227
TAJO-1157: Required Java version in tutorial doc needs to be updated.

Closes #230
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1149
add some description for EmptyTuple