class method self.normalize_key

# File activesupport/lib/active_support/vendor/i18n-0.4.1/i18n.rb, line 305
    def normalize_key(key, separator)
      normalized_key_cache[separator][key] ||=
        case key
        when Array
          key.map { |k| normalize_key(k, separator) }.flatten
        else
          keys = key.to_s.split(separator)
          keys.delete('')
          keys.map!{ |k| k.to_sym }
          keys
        end
    end