Never pass three arguments to $.each because it breaks things badly

The three argument `$.each` is only for internal use in jQuery. The current code results in both `key` and `value` being undefined in each iteration so all `_options` are ignored and only `defaults` are used.

See also inline comments in https://github.com/twitter/bootstrap/commit/01e0f8c653db442326ee1559eac4691af246d49e