Godeps/_workspace/src/gopkg.in/mgo.v2/bson/bson.go
func (id ObjectId) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf(`"%x"`, string(id))), nil
}
func (id ObjectId) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf(`"%x"`, string(id))), nil
}
// MarshalJSON turns a bson.ObjectId into a json.Marshaller.