TAJO-1070: BSTIndexScanExec should not seek a negative offset. (jinho)

Closes #159
TAJO-1060: Apply updated hadoop versions to README and BUILDING files. (jinho)

Closes #158
TAJO-1061: Update build documentation. (jaehwa)

Closes #157
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1067