datastore: Update AllocateIDs to take keys.

filter/txnBuf/txnbuf_test.go

Index: filter/txnBuf/txnbuf_test.go
diff --git a/filter/txnBuf/txnbuf_test.go b/filter/txnBuf/txnbuf_test.go
index aabdc5ed839bbfd29a2361eb9de507968b20eb52..7c0565940513b3f5b554e4616757c74e76b9a306 100644
--- a/filter/txnBuf/txnbuf_test.go
+++ b/filter/txnBuf/txnbuf_test.go
@@ -130,8 +130,9 @@ func init() {
 func mkds(data []*Foo) (under, over *count.DSCounter, ds datastore.Interface) {
 	c := memory.UseWithAppID(context.Background(), "something~else")
 	ds = datastore.Get(c)
-	_, err := ds.AllocateIDs(ds.KeyForObj(data[0]), 100)
-	if err != nil {
+
+	dataKey := ds.KeyForObj(data[0])
+	if err := ds.AllocateIDs(ds.NewIncompleteKeys(100, dataKey.Kind(), dataKey.Parent())); err != nil {
 		panic(err)
 	}
 	if err := ds.PutMulti(data); err != nil {