all: fix shadowing bugs found by go tool vet -shadow

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/10328044

src/pkg/net/http/transport_test.go

@@ -553,12 +553,13 @@ func TestRoundTripGzip(t *testing.T) {
 		res, err := DefaultTransport.RoundTrip(req)
 		var body []byte
 		if test.compressed {
-			gzip, err := gzip.NewReader(res.Body)
+			var r *gzip.Reader
+			r, err = gzip.NewReader(res.Body)
 			if err != nil {
 				t.Errorf("%d. gzip NewReader: %v", i, err)
 				continue
 			}
-			body, err = ioutil.ReadAll(gzip)
+			body, err = ioutil.ReadAll(r)
 			res.Body.Close()
 		} else {
 			body, err = ioutil.ReadAll(res.Body)

src/pkg/os/file_unix.go

@@ -158,9 +158,10 @@ func (f *File) readdir(n int) (fi []FileInfo, err error) {
 	names, err := f.Readdirnames(n)
 	fi = make([]FileInfo, len(names))
 	for i, filename := range names {
-		fip, err := Lstat(dirname + filename)
+		fip, lerr := Lstat(dirname + filename)
 		if err == nil {
 			fi[i] = fip
+			err = lerr
 		} else {
 			fi[i] = &fileStat{name: filename}
 		}