reflect: fix test failure reporting.

There's a problem that is manifesting on the 386 builders,
but this test bug is masking it.

R=adg
CC=golang-dev
https://golang.org/cl/5295042

src/pkg/reflect/all_test.go

@@ -887,7 +887,7 @@ func TestMap(t *testing.T) {
 		if i >= len(keys) {
 			t.Errorf("Missing key #%d %q", i, k)
 		} else if kv := keys[i]; kv.String() != k {
-			t.Errorf("Keys[%q] = %d, want %d", i, kv.Int(), k)
+			t.Errorf("Keys[%q] = %q, want %q", i, kv.String(), k)
 		}
 		i++