rename bytes.Buffer.Data() to bytes.Buffer.Bytes()

R=rsc
DELTA=152  (6 added, 0 deleted, 146 changed)
OCL=34695
CL=34701
diff --git a/src/pkg/bufio/bufio_test.go b/src/pkg/bufio/bufio_test.go
index 58e4456..78920eb 100644
--- a/src/pkg/bufio/bufio_test.go
+++ b/src/pkg/bufio/bufio_test.go
@@ -256,7 +256,7 @@
 				t.Errorf("%s: buf.Flush = %v", context, e);
 			}
 
-			written := w.Data();
+			written := w.Bytes();
 			if len(written) != nwrite {
 				t.Errorf("%s: %d bytes written", context, len(written));
 			}
@@ -372,7 +372,7 @@
 		t.Error("WriteString", b.err);
 	}
 	s := "01234567890abcdefghijklmnopqrstuvwxyz";
-	if string(buf.Data()) != s {
-		t.Errorf("WriteString wants %q gets %q", s, string(buf.Data()))
+	if string(buf.Bytes()) != s {
+		t.Errorf("WriteString wants %q gets %q", s, string(buf.Bytes()))
 	}
 }