goprotobuf: Add Merge.

R=adg
CC=golang-dev
https://codereview.appspot.com/7227053
diff --git a/proto/all_test.go b/proto/all_test.go
index c3b2378..9c9cf0f 100644
--- a/proto/all_test.go
+++ b/proto/all_test.go
@@ -1427,7 +1427,7 @@
 	}
 }
 
-func TestMerge(t *testing.T) {
+func TestMergeMessages(t *testing.T) {
 	pb := &MessageList{Message: []*MessageList_Message{{Name: String("x"), Count: Int32(1)}}}
 	data, err := Marshal(pb)
 	if err != nil {