storage/sql: rework of the original MySQL PR

vendor/github.com/go-sql-driver/mysql/appengine.go

@@ -0,0 +1,19 @@
+// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
+//
+// Copyright 2013 The Go-MySQL-Driver Authors. All rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build appengine
+
+package mysql
+
+import (
+	"google.golang.org/appengine/cloudsql"
+)
+
+func init() {
+	RegisterDial("cloudsql", cloudsql.Dial)
+}