HPCC-9244 - Improved LOOKUP,MANY scheme

LOOKUP MANY was horrendously slow if there were truly many
duplicates. New scheme avoids pathogenic case and also improves
efficiency of ATMOST processing.

Refactored All vs LOOKUP vs LOOKUP MANY implementations

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4980 from jakesmith/hpcc-9244

HPCC-9244 - Improved LOOKUP,MANY scheme

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>