datastore: Add DecodeCursor to [Raw]Interface.

impl/memory/datastore.go

Index: impl/memory/datastore.go
diff --git a/impl/memory/datastore.go b/impl/memory/datastore.go
index 857b06e307a686b38eef483c4e650fb3467ea6b3..2e78c129eb7014c144cccb5b499cc8e1ff981d07 100644
--- a/impl/memory/datastore.go
+++ b/impl/memory/datastore.go
@@ -68,6 +68,10 @@ func (d *dsImpl) NewQuery(kind string) ds.Query {
 	return &queryImpl{ns: d.ns, kind: kind}
 }
 
+func (d *dsImpl) DecodeCursor(s string) (ds.Cursor, error) {
+	return decodeCursor(s)
+}
+
 func (d *dsImpl) Run(q ds.Query, cb ds.RawRunCB) error {
 	rq := q.(*queryImpl)
 	done, err := rq.valid(d.ns, true)
@@ -141,6 +145,10 @@ func (d *txnDsImpl) DeleteMulti(keys []ds.Key, cb ds.DeleteMultiCB) error {
 	})
 }
 
+func (d *txnDsImpl) DecodeCursor(s string) (ds.Cursor, error) {
+	return decodeCursor(s)
+}
+
 func (d *txnDsImpl) Run(q ds.Query, cb ds.RawRunCB) error {
 	rq := q.(*queryImpl)
 	done, err := rq.valid(d.ns, true)