net: remove duplicate error information in Dial

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5293045

src/pkg/net/dial.go

@@ -59,10 +59,10 @@ func Dial(net, addr string) (c Conn, err os.Error) {
 	case *IPAddr:
 		c, err = DialIP(net, nil, ra)
 	default:
-		err = UnknownNetworkError(net)
+		err = &OpError{"dial", net + " " + addr, nil, UnknownNetworkError(net)}
 	}
 	if err != nil {
-		return nil, &OpError{"dial", net + " " + addr, nil, err}
+		return nil, err
 	}
 	return
 }

src/pkg/net/net_test.go

@@ -62,6 +62,8 @@ var dialErrorTests = []DialErrorTest{
 	},
 }
 
+var duplicateErrorPattern = `dial (.*) dial (.*)`
+
 func TestDialError(t *testing.T) {
 	if !*runErrorTest {
 		t.Logf("test disabled; use --run_error_test to enable")
@@ -81,6 +83,10 @@ func TestDialError(t *testing.T) {
 		if !match {
 			t.Errorf("#%d: %q, want match for %#q", i, s, tt.Pattern)
 		}
+		match, _ = regexp.MatchString(duplicateErrorPattern, s)
+		if match {
+			t.Errorf("#%d: %q, duplicate error return from Dial", i, s)
+		}
 	}
 }