get rid of chunked iterators for facts.

src/prolog/fixtures.rs

@@ -173,11 +173,11 @@ impl<'a> VariableFixtures<'a>
 
     pub fn mark_vars_in_chunk<Iter>(&mut self,
                                     iter: Iter,
-                                    last_term_arity: usize,
-                                    chunk_num: usize,
+                                    last_term_arity: usize,                                    
                                     term_loc: GenContext)
         where Iter: Iterator<Item=TermRef<'a>>
     {
+        let chunk_num = term_loc.chunk_num();
         let mut arg_c = 1;
 
         for term_ref in iter {