BUG/MEDIUM: tasks: Make sure we set TASK_QUEUED before adding a task to the rq.

BUG/MEDIUM: tasks: Make sure we set TASK_QUEUED before adding a task to the rq.

Make sure we set TASK_QUEUED in every case before adding the task to the
run queue. task_wakeup() now checks if either TASK_QUEUED or TASK_RUNNING
is set, and if neither is set, add TASK_QUEUED and effectively add the task
to the runqueue.
No longer use __task_wakeup() anywhere except in task_wakeup(), always use
task_wakeup() instead.
With the old code, process_runnable_task() may re-add a task in the runqueue
without setting the TASK_QUEUED flag, and there were race conditions that could
lead to a task having the TASK_QUEUED flag but not in the runqueue, thus
being unschedulable.

This should be backported to 1.9.