public void AddOption (FieldInfo field, OptionAttribute option)
{
Pair pair = new Pair (target_object);
pair.Field = field;
pair.Option = option;
all_pairs.Add (pair);
if (option.Name != null)
by_name [option.Name] = pair;
if (option.LongName != null)
by_long_name [option.LongName] = pair;
}