properly.
MCOL-894 Unit tests to build a framework for a new parallel sorting.
MCOL-894 Finished with parallel workers invocation.
The implementation lacks final aggregation step.
MCOL-894 TupleAnnexStep's init and destructor are now parallel execution aware.
Implemented final merging step for parallel execution finalizeParallelOrderBy().
Templated unit test to use it with arbitrary number of rows, threads.
Reuse LimitedOrderBy in the final step
MCOL-894 Cleaned up finalizeParallelOrderBy.
MCOL-894 Add and propagate thread variable that controls a number of threads.
Optimized comparators used for sorting and add corresponding UTs.
Refactored TupleAnnexStep::finalizeParallelOrderByDistinct.
Parallel sorting methods now preallocates memory in batches.
MCOL-894 Fixed comparator for StringCompare.
b/c an incorrect number of key columns was used whilst
initializing Eq() struct. The regression caused by
changes made for MCOL-1829 so I revised the changes
made. Now LimitedOrderBy::getKeyLength() returns an
actual key columns count.
