core: fix bench and ignore form, because they were buggy

core/Bench.carp

@@ -27,7 +27,7 @@
   (defn ns-iter-inner [f n]
     (let [start (get-time-elapsed)]
       (do
-        (for [i 0 n] (ignore f))
+        (for [i 0 n] (ignore (f)))
         (Double.- (get-time-elapsed) start))))
 
   (defn print-bench-results [res total]

core/Macros.carp

@@ -196,4 +196,4 @@
   (list 'IO.println (list 'ref (build-str* forms))))
 
 (defmacro ignore [form]
-  (let [_ form] ()))
+  (list 'let (array '_ form) (list)))