Add word separator for AR error messages

Hi. I'm a Japanese Railer. I tried I18n translation on Rails 2.2.0, and felt a slight discomfort in the translated Japanese text.

For example, with a resource file like this,

ja-JP:
  activerecord:
    models:
      user: ユーザー
    attributes:
      user:
        name: 名前
    errors:
      messages:
        blank: を入力してください。

I got following validation error message.

名前 を入力してください。

This seems 90% okay, but as we Japanese usually don't separate words by space, we prefer a string like this.

名前を入力してください。

This patch enables to configure delimiter string for each locale (no test code yet, sorry).

ja-JP:
  activerecord:
    errors:
      format:
        # Sets the separator between the words
        separator: ""

This makes "my" app speak perfect Japanese (and maybe some other Asian languages like Chinese, Korean, Thai, Burmese, etc.), but I know it's not really a good design for all other developers... (they won't notice this parameter until they read the source code) So, any other better implementation idea are welcomed.