TAJO-991: Running PullServer on a dedicated JVM process which separates from worker.

Closes #107
TAJO-1017: TajoConf misuses read & write locks in some functions. (Mai Hai Thanh via hyunsik)

Closes #130
TAJO-937: Should use tajo.util.VersionInfo instead of TajoConstants.TAJO_VERSION. (Mai Hai Thanh via hyunsik)

Closes #131
TAJO-1010: Improve multiple DISTINCT aggregation.

TupleComparator thread safe
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1010