I18n fix on error_messages_for and allow strings to be sent as collection to select

Guys,

1. Fixes a bug where error_messages_for looks for "book seller" names
in I18n when it should look for "book_seller".

https://rails.lighthouseapp.com/projects/8994/tickets/2390-object-names-with-underscore-do-the-wrong-lookup-in-i18n-on-error_messages_for

2. Allow strings to be sent to select in order to use nested attribute
goodness.

https://rails.lighthouseapp.com/projects/8994/tickets/2391-allow-strings-to-be-sent-as-collection-to-select

Regards,