Revert PIG-3434: Null subexpression in bincond nullifies outer tuple (or bag)

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PIG-3483: Document ASSERT keyword

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PIG-3445: Make Parquet format available out of the box in Pig (lbendig via aniket486)

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PIG-3497: JobControlCompiler should only do reducer estimation when the job has a reduce phase (amatsukawa via aniket486)

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