impl/memory: Fix time serialization encoding.

service/datastore/properties.go

Index: service/datastore/properties.go
diff --git a/service/datastore/properties.go b/service/datastore/properties.go
index d82118dbe77eee6c75db7ddb90f0fd227f635e8f..a81b0ee3652075464b28934197903fecfc9f7c31 100644
--- a/service/datastore/properties.go
+++ b/service/datastore/properties.go
@@ -245,6 +245,12 @@ func PropertyTypeOf(v interface{}, checkValid bool) (PropertyType, error) {
 	}
 }
 
+// RoundTime rounds a time.Time to microseconds, which is the (undocumented)
+// way that the AppEngine SDK stores it.
+func RoundTime(t time.Time) time.Time {
+	return t.Round(time.Microsecond)
+}
+
 // timeLocationIsUTC tests if two time.Location are equal.
 //
 // This is tricky using the standard time API, as time is implicitly normalized