- Explained how to override the default load order of metal apps
  - Explained that metal apps within plugins will also be loaded

Beefed up mass assignment coverage (section 6) in the security guide.  Now includes nested mass assignment (and nested object forms) and adds another (paranoid) countermeasure.

Fixed incorrect examples of ActiveRecord error message lookup in the I18N guide [Thanks Alex Fortuna]

See http://www.ruby-forum.com/topic/179273

Clarified info about "pragmatic approach to locale codes" and removed speculation about "locale inheritance" in the I18N guide [thanks Kip]

See http://groups.google.com/group/rails-i18n/msg/7b4513b3ca8abbf5

See:

* http://github.com/rails/rails/commit/a98cd7ca9b2f24a4500963e58ba5c37d6bdf9259
* http://afreshcup.com/2009/02/01/rails-23-localized-views/

Added note how to configure Rails loading mechanism to look for nested locale files (+config/locales/models/book/es.yml+, etc) to the I18N guide

TODOS are in http://rails.lighthouseapp.com/projects/16213/tickets/23-rails-i18