Complete threading chapter

I hope you have time to finish it, Mik :)

Well, I finally worked out how to do this.. it works for me.

All the nodes need to share the same fiber, plus there has to be some way of passing back the element on each visit, so I decided to pass another class instance as the fiber object.

Tidied up the visitor's calling

Thought up a little improvement over lunch ;)

Example:

./fiberContainer 10 400 90 5 2 8
All values less than 100:
value: 2
value: 5
value: 8
value: 10
value: 90

I presume it's perfectly acceptable to destroy a Fiber when its function has partially run but not completed.

Lars/tango devs: Fiber.call's return value indicating whether or not the fiber has finished strikes me as more useful than returning an exception in general. Of course some way of getting exceptions back may be necessary, but a second little call function like mine (but renamed) could be quite useful. Minor point though.