when addin stack 2 stack reference - check that position is within valid
range (on stack)
undo self reference option - was not working anyway ;-)
Move the function data (VALFUNC) off from BINDING_DATA;
reason: the structure for function (VALFUNC) was becoming too large, as
a result the data value was becoming too large. Also the reference
from function data to collection was wrong (pointer to stack element
would be invalidated when stack was resized / grows).
Major milestone: Pooh now supports linked lists (slist.inc - single
linked lists)