cleanups in syntax.scm

* benchmark/lib.scm (fibo): Make fibo actually a fibonacci sequence.

* module/system/base/syntax.scm (system): Forward-declare all exports.
  (expand-symbol, slot): Rewrite expand-symbol to expand to a
  non-recursive invocation of `slot', so that in the future when we get
  rid of this syntax, the replacement will be more palatable to the eyes.

benchmark/lib.scm

@@ -4,10 +4,10 @@
 
 
 (define (fibo x)
-  (if (= 1 x)
+  (if (or (= x 1) (= x 2))
       1
-      (+ x
-	 (fibo (1- x)))))
+      (+ (fibo (- x 1))
+	 (fibo (- x 2)))))
 
 (define (g-c-d x y)
   (if (= x y)