Interface update, per-method Contexts.

service/datastore/raw_interface.go

Index: service/datastore/raw_interface.go
diff --git a/service/datastore/raw_interface.go b/service/datastore/raw_interface.go
index 96e54d3370311ffb63b4a2e01065ab94d0a2bc80..481acf7a99896a9bdfec2e46057b052fa5cebef4 100644
--- a/service/datastore/raw_interface.go
+++ b/service/datastore/raw_interface.go
@@ -184,7 +184,15 @@ type RawInterface interface {
 	//   - cb is not nil
 	DeleteMulti(keys []*Key, cb DeleteMultiCB) error
 
-	// Testable returns the Testable interface for the implementation, or nil if
-	// there is none.
-	Testable() Testable
+	// WithTransaction, given a Context, returns a derived Context with the
+	// supplied datastore Transaction installed.
+	WithTransaction(Transaction) context.Context
+
+	// CurrentTransaction returns a reference to the current Transaction, or nil
+	// if the Context does not have a current Transaction.
+	CurrentTransaction() Transaction
+
+	// GetTestable returns the Testable interface for the implementation, or nil
+	// if there is none.
+	GetTestable() Testable
 }