use fixnums in place of bignums where possible

src/prolog/lib/assoc.pl

@@ -63,12 +63,12 @@ Assocs are Key-Value associations implemented as  a balanced binary tree
 @author         R.A.O'Keefe, L.Damas, V.S.Costa and Jan Wielemaker
 */
 
-/*					  
+/*
 :- meta_predicate
     map_assoc(1, ?),
     map_assoc(2, ?, ?).
 */
-					  
+
 %!  empty_assoc(?Assoc) is semidet.
 %
 %   Is true if Assoc is the empty association list.