In order to authorize call of task_wakeup on running task:
- from within the task handler itself.
- in futur, from another thread.
The lookups on runqueue and waitqueue are re-worked
to prepare multithread stuff.
If task_wakeup is called on a running task, the woken
message flags are savec in the 'pending_state' attribute of
the state. The real wakeup is postponed at the end of the handler
process and the woken messages are copied from pending_state
to the state attribute of the task.
It's important to note that this change will cause a very minor
(though measurable) performance loss but it is necessary to make
forward progress on a multi-threaded scheduler. Most users won't
ever notice.
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