HPCC-7902 - Add DISTRIBUTED,ASSERT implementation

Validates that input dataset is distributed

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
HPCC-7902 - Output row that was not distributed in error

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5087 from jakesmith/hpcc-7902

HPCC-7902 - Add DISTRIBUTED,ASSERT implementation

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>