drill

5f34c960 - DRILL-4927 (part 2): Add support for Null Equality Joins (mixed comparators)

DRILL-4927 (part 2): Add support for Null Equality Joins (mixed comparators) This changes are a subset of the original pull request from DRILL-4539 (PR-462). - Added changes to support mixed comparators; - Added tests for it. closes #635