HPCC-9015 Restore previous ROLLUP semantics

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4164 from ghalliday/issue9015a

HPCC-9015 Restore previous ROLLUP semantics

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>