move ReadFile, WriteFile, and ReadDir into a separate io/ioutil package.
this breaks the dependency of package io on package bytes.

R=rsc
CC=golang-dev
https://golang.org/cl/163085
diff --git a/test/bench/k-nucleotide.go b/test/bench/k-nucleotide.go
index d256b37..47debec 100644
--- a/test/bench/k-nucleotide.go
+++ b/test/bench/k-nucleotide.go
@@ -39,7 +39,7 @@
 	"bufio";
 	"bytes";
 	"fmt";
-	"io";
+	"io/ioutil";
 	"os";
 	"sort";
 	"strings";
@@ -122,7 +122,7 @@
 			break
 		}
 	}
-	data, err := io.ReadAll(in);
+	data, err := ioutil.ReadAll(in);
 	if err != nil {
 		fmt.Fprintln(os.Stderr, "ReadAll err:", err);
 		os.Exit(2);