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