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A runtime mechanism is already available (PyOS_CheckStack), 
but it is only used on platforms where a stack overrun would be 
disastrous (i.e. run into your heap in stead of giving a SEGV), 
because it is pretty expensive. If there is a common way to do 
this easier (i.e. set a red zone pointer and do one pointer 
compare in a stack test macro) I would be all for it, bt I don't 
know how to do this.