Don't put structure cells on the heap
This is the first optimization in chapter 5.  It seems to help a little bit, and
is almost trivial to implement.  Cool.
    
        | author | Steve Losh <steve@stevelosh.com> | 
    
        | date | Tue, 10 May 2016 19:05:13 +0000 | 
    
    
        | parents | 9becedc43e4d | 
    
        | children | 0a4b04d4dfa7 | 
    
        | branches/tags | (none) | 
    
        | files | src/wam/vm.lisp | 
Changes
    
--- a/src/wam/vm.lisp	Tue May 10 00:05:11 2016 +0000
+++ b/src/wam/vm.lisp	Tue May 10 19:05:13 2016 +0000
@@ -248,8 +248,8 @@
      (functor functor-index)
      (register register-index))
   (setf (wam-local-register wam register)
-        (push-new-structure! wam))
-  (push-new-functor! wam functor))
+        (make-cell-structure
+          (nth-value 1 (push-new-functor! wam functor)))))
 
 (define-instructions (%set-variable-local %set-variable-stack)
     ((wam wam)