Reduce runqueue lock contention -v2

Hi, here a new posting of my scary patch(es) ;-)

These actually survive a sembench run (and everything else I threw at it).
The discussion between Mike and Frank over the task_running() check made me
realize what was wrong with the previous one.

As it turns out, what was needed (p->oncpu) was something Thomas wanted me
to do for an entirely different reason (see patch #2).

Frank's patch, while encouraging me to poke at it again, has a number of
very fundamental problems with it, the most serious one being that it
completely wrecks the wake-up load-balancing.

I'll try and come up with a way to unwreck the 32bit select_task_rq_fair()
problem, but for now inspiration in that departments seems lacking, yet I
still wanted to share these patches so that others can have a go at them.

If all you care about is the numbers, skip to patch #5.

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