func (file *GridFile) GetMeta(result interface{}) (err error) {
	file.m.Lock()
	if file.doc.Metadata != nil {
		err = bson.Unmarshal(file.doc.Metadata.Data, result)
	}
	file.m.Unlock()
	return
}
func (file *GridFile) GetMeta(result interface{}) (err error) {
	file.m.Lock()
	if file.doc.Metadata != nil {
		err = bson.Unmarshal(file.doc.Metadata.Data, result)
	}
	file.m.Unlock()
	return
}
// GetMeta unmarshals the optional "metadata" field associated with the
// file into the result parameter. The meaning of keys under that field
// is user-defined. For example:
//
//     result := struct{ INode int }{}
//     err = file.GetMeta(&result)
//     if err != nil {
//         panic(err.String())
//     }
//     fmt.Printf("inode: %d\n", result.INode)
//