http: correct format flags when printing errors during tests

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/4809065

src/pkg/http/fs_test.go

@@ -223,7 +223,7 @@ func TestServeFileContentType(t *testing.T) {
 			t.Fatal(err)
 		}
 		if h := resp.Header.Get("Content-Type"); h != want {
-			t.Errorf("Content-Type mismatch: got %d, want %d", h, want)
+			t.Errorf("Content-Type mismatch: got %q, want %q", h, want)
 		}
 	}
 	get("text/plain; charset=utf-8")
@@ -257,7 +257,7 @@ func TestServeFileWithContentEncoding(t *testing.T) {
 		t.Fatal(err)
 	}
 	if g, e := resp.ContentLength, int64(-1); g != e {
-		t.Errorf("Content-Length mismatch: got %q, want %q", g, e)
+		t.Errorf("Content-Length mismatch: got %d, want %d", g, e)
 	}
 }