DRILL-1549: Partition pruning for simple IN filters.
DRILL-1534: Implement Mappify UDF to transform map into a repeated map with key, value pairs
DRILL-1511: C++ Client. Fix compiling issues in DRILL-1297 patch.

- Remove forward enum type declaration (not allowed in C++ 03).
- Add space between `<` and `::` to fix compilation of clang
DRILL-1305: C++ Client. Consume QueryState message from the Drillbit.
DRILL-1417: ensure star column is passed to scan in case non-partition columns are empty