goprotobuf: Fix SetDefaults to recur into repeated submessages.

R=r
CC=golang-dev
https://codereview.appspot.com/11255043
diff --git a/proto/all_test.go b/proto/all_test.go
index 6478c57..9d51158 100644
--- a/proto/all_test.go
+++ b/proto/all_test.go
@@ -1341,6 +1341,21 @@
 	}
 }
 
+func TestSetDefaultsWithRepeatedSubMessage(t *testing.T) {
+	m := &MyMessage{
+		RepInner: []*InnerMessage{{}},
+	}
+	expected := &MyMessage{
+		RepInner: []*InnerMessage{{
+			Port: Int32(4000),
+		}},
+	}
+	SetDefaults(m)
+	if !Equal(m, expected) {
+		t.Errorf("\n got %v\nwant %v", m, expected)
+	}
+}
+
 func TestMaximumTagNumber(t *testing.T) {
 	m := &MaxTag{
 		LastField: String("natural goat essence"),