HPCC-9698 - Can't run more than one thor job that uses R

R crashes if it is unloaded/reloaded.
Which Thor will do per job.
Avoid by effectively leaking the library, by getting libRembed to
dynamically load itself on startup.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Fix comments
Merge pull request #4639 from jakesmith/hpcc-9698

HPCC-9698 - Can't run more than one thor job that uses R

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>