Lisp accessors for PL-ITERATOR values.

Just to close out this discussion, since there was a wrinkle I had  
forgotten about:

PowerLoom's lisp translation comes in two versions, one which uses  
CLOS objects to implement the Stella/PowerLoom objects and one which  
uses structs (defstruct) instead.  The default release uses structs  
for speed.  But the accessors for slots look different in the CLOS  
and the STRUCT version.

In the CLOS version, values from Pl-iterator are accessed using the  
generic function "%value", which works for all iterators and is  
always in the STELLA package.

In the Struct version, values from Pl-iterator are accessed using the  
function "%pl-iterator.value" in the PLI package, which works only on  
pl-iterators.  Other iterators have their own, specially qualified  
names that are used to get the values, generally in the STELLA package.

So that means that if you write lisp code to manipulate pl-iterators,  
you need to be aware of this distinction.  For the more common Struct  
case, you could iterator through all concepts by doing something like:


   (let ((iter (pli:s-retrieve "all (concept ?x)" "PL-USER" null)))
     (loop while (stella::next? iter)
           do (print (pli::%pl-iterator.value iter))))