thorium: set status to THORIUM_SCHEDULER_STATUS_SCHEDULED initially

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: enqueue message before scheduling actor

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: thorium_worker_schedule_actor is now a public function

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use thorium_worker_schedule_actor to inject a cached message

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use thorium_worker_schedule_actor to schedule messages

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: don't schedule already-scheduled actor

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>