SetItemStackSize

// Sets stack size of an item.
// - oItem: item to change
// - nSize: new size of stack.  Will be restricted to be between 1 and the
//   maximum stack size for the item type.  If a value less than 1 is passed it
//   will set the stack to 1.  If a value greater than the max is passed
//   then it will set the stack to the maximum size
void SetItemStackSize(object oItem, int nSize);