Add license and comment.

backup.go

@@ -1,3 +1,19 @@
+/*
+ * Copyright 2017 Dgraph Labs, Inc. and Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package badger
 
 import (

transaction.go

@@ -31,6 +31,7 @@ import (
 )
 
 type oracle struct {
+	// curRead must be at the top for memory alignment. See issue #311.
 	curRead   uint64 // Managed by the mutex.
 	refCount  int64
 	isManaged bool // Does not change value, so no locking required.