TAJO-880: NULL in CASE clause occurs Exception. (Hyoungjun Kim via hyunsik)

 Closes #40
TAJO-848: PreLogicalPlanVerifier::visitInsert need to find smaller expressions than target columns for a partitioned table. (jaehwa)
TAJO-879: Some data is missing in the case of BROADCAST JOIN and multi-column partition. (Hyoungjun Kim via jaehwa)
TAJO-850: OUTER JOIN does not properly handle a NULL. (Hyoungjun Kim via hyunsik)

Closes #22
TAJO-853: Refactoring FilterPushDown for OUTER JOIN. (Hyoungjun Kim via hyunsik)

Closes #28
TAJO-886: Add IRC page to community section in site.

Closes #45
TAJO-882: CLI hangs when a error occurs in the GlobalPlanner. (Hyoungjun Kim via hyunsik)

Closes #42
Merge branch 'master' of http://git-wip-us.apache.org/repos/asf/tajo into selection-down