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-1028: JDBC should support SET command.

Closes #135
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1027
TAJO-1029: TAJO_PULLSERVER_STANDALONE should be false in default tajo-env.sh. (jinho)

Closes #134
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1027