all: fix some mistakes found by go tool vet .

R=golang-dev, iant, adg
CC=golang-dev
https://golang.org/cl/14000043
diff --git a/src/pkg/math/big/int_test.go b/src/pkg/math/big/int_test.go
index 01d5d4e..87b975d 100644
--- a/src/pkg/math/big/int_test.go
+++ b/src/pkg/math/big/int_test.go
@@ -89,7 +89,7 @@
 	var z Int
 	f(&z, a.x, a.y)
 	if !isNormalized(&z) {
-		t.Errorf("%s%v is not normalized", z, msg)
+		t.Errorf("%s%v is not normalized", msg, z)
 	}
 	if (&z).Cmp(a.z) != 0 {
 		t.Errorf("%s%+v\n\tgot z = %v; want %v", msg, a, &z, a.z)