HPCC-8881 Move roxierow into thorhelper dll

Fix confusing namespace, and move a couple of defines back to roxiemem

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4026 from richardkchapman/roxierow-move

HPCC-8881 Move roxierow into thorhelper dll

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>