DRILL-810 : add isSafe() to Nullable value vector. Check nullable value vector has capacity for new value in run-time code.
setSafe() in variable length vector should check has capacity to hold new value.
Bug fixes in Project operator. Use allocateNewSafe() to allocate space for outgoing batch in Project.

Reenable testcase.
copy unmerged records in merge sort to new buffer
Drill 649: Reading impala and avro generated parquet files

Implemented dictionary encoding for the non-varlength types.
Drill 816: Fix bug with reading nullable columns resulting in mismatched number of records in vectors.