now the SAH building strategy is responsible to allocate 8-byte aligned
memory for the TriangleIterator begin and end.
The code to allocated the memory is already inserted. This affected one
line in the building-strategy.
This can't be done in the FastKdTree, because anyway we would need to
save the pointer to the FastKdTreeMemoryAllocator which makes the
FastKdTree bigger.

The FastKdTreeMemoryAllocator now saves beside the FastKdTree-Array and
array for the iterators. And the FastKdTreeMemoryAllocator has got a
method to insert the next to iterator as object into the allocated
memory space and retunr the pointer to the iterator begin.

Changed the FastKdTree structure that it only has a method to save the
pointer to the memory where the TriangleIterator begin is (called
setTriangleIteratorBegin(...). The next higher adress should be the
TriangleIterator end then, when the iterators were allocated via the
FastKdTreeMemoryAllocator. So this pointer can be saved.

The iterator object as such cannot be saved inside the kdtree, because
it could possibly use the lower 3 bits which are needed inside the
kdtree and must not be overwritten!
The tterators (begin and end) are not well stored. They are destroyed
after the SAH-strategy ran. => FastKdTree is not build correctly yet
Peter will check this.