Add GetNoTxn to txnBuf as a hack.

filter/txnBuf/context.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package txnBuf
 
 import (
         "golang.org/x/net/context"
 
         ds "github.com/luci/gae/service/datastore"
@@ skipping 27 matching lines @@
         }
 }
 
 // memoryCorruption is a marker function to indicate that given error is
 // actually due to corrupted memory to make it easier to read the code.
 func memoryCorruption(err error) {
         if err != nil {
                 panic(err)
         }
 }
+
+// GetNoTxn allows you to to escape the buffered transaction (if any), and get
+// a non-transactional handle to the datastore. This does not invalidate the
+// currently-buffered transaction, but it also does not see any effects of it.
+//
+// TODO(iannucci): This is messy, but mostly because the way that transactions
+// work is messy. Fixing luci/gae#issues/23 would help though, because it means
+// we could make transactionality recorded by a single index in the context
+// instead of relying on function nesting.
+func GetNoTxn(c context.Context) ds.Interface {
+        c = context.WithValue(c, dsTxnBufParent, nil)
+        c = context.WithValue(c, dsTxnBufHaveLock, nil)
+        return ds.GetNoTxn(c)
+}