Flags

The logic:

```ruby
unless flag then @unknown_argvs << flag ; next ; end
```

does not work correctly. Only when the condition is met will `flag` be added to `@unknown_argvs`, however, in order for the condition to *be* met, `flag` must be `nil`, which then stores a `nil` value in `@unknown_argvs`. This will not help indicate any unknown flags that may have been passed on the command line.