For ENG-4883, handle duplicate rows during safe restore when loading/converting replicated data
For ENG-4883 based on Wei Wei's feedback, make unique violations with a null duplicate row handler a hard failure
For ENG-4883, fix bug where the output buffer for duplicates was not initialized empty
For ENG-4883, more cleanup based on review. Factor out common code to a helper
For ENG-4883, test that a snapshot restore without duplicate handling fails as expected
Merge pull request #703 from VoltDB/ENG-4883

For ENG-4883, handle duplicate rows during safe restore when loading/con...