goprotobuf: Better enum construction.

R=r
CC=golang-dev
http://codereview.appspot.com/6188053
diff --git a/proto/text_test.go b/proto/text_test.go
index f09b1ab..049eded 100644
--- a/proto/text_test.go
+++ b/proto/text_test.go
@@ -65,7 +65,7 @@
 				},
 			},
 		},
-		Bikeshed: pb.NewMyMessage_Color(pb.MyMessage_BLUE),
+		Bikeshed: pb.MyMessage_BLUE.Enum(),
 		Somegroup: &pb.MyMessage_SomeGroup{
 			GroupField: proto.Int32(8),
 		},