Support for updating a belongs to association from the foreign key (without saving and reloading the record)

Hi all,

I would like to solicit feedback for this ticket: #142 belongs_to association not updated when assigning to foreign key - Ruby on Rails - rails. The reasoning is explained in the ticket so I won't repeat that here but I would like to hear any opinions on why this should or should not be applied.

The latest patch (as of today) is available here: http://rails.lighthouseapp.com/attachments/44268/belongs_to_update_association_from_foreign_key.diff

Cheers, Jon