DRILL-1838: MapVector should late bind/replace vector if current vector is null valued
DRILL-1839: Clean up complex writers per batch if project has a ComplexWriter function evaluation
DRILL-1843: Support per-batch schema change at RecordBatchLoader
DRILL-1845: Do not pass partition columns to parquet reader
DRILL-1848: Specify value of MAX_QUERY_MEMORY_PER_NODE_KEY in bytes instead of MB. Fixes the external sort running out of memory.
DRILL-1846: Use max receiver width during stats collection for parallelism planning.  SingleMergeExchange and UnionExchange have a max receive width of 1.  Others can go higher.