No more worker-thread workspace

[Poul-Henning Kamp]

I have completed the much mumbled about move of the thread workspace
to busyobj.  This should save a fair amount of memory and thread-stack.

A quick experiment showed that I could run the test-cases with only
32k of thread-stack.

See commit messages for more details.

Feedback welcome.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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Never attribute to malice what can adequately be explained by incompetence.