TAJO-1025: Network disconnection during query processing can cause infinite exceptions. (Jihun Kang via jinho)
TAJO-983: Worker should directly read Intermediate data stored in localhost rather than fetching. (Mai Hai Thanh via hyunsik)
TAJO-1070: BSTIndexScanExec should not seek a negative offset. (jinho)

Closes #159
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1060
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