Add a rexx instance option, THREAD_ISOLATION, that turns off the checking of the callers thread ID for the RexxExitContext.
I see this mainly allowing a command exit, that is multi threaded, access to the context variable pool. It would be the users
responsibility to ensure that only a signal thread calls the API at a time.
I would apply this check only in the "inline ApiContext(RexxExitContext *c)" method. That way any interal calls to validate the thread ID
would ignore the option setting.
The default option setting would of course be TRUE, thus enabling current behaviour.