New update_attribute doesn't work with associations

Previous implementation of update_attribute:

def update_attribute(name, value)
  send("#{name}=", value)
  save(false)
end

worked just fine with associations.

The one present in current master breaks this support:

Consider this call:

article.update_attribute(:user, user)

Let's go through the method definition:

def update_attribute(name, value)     
  changes = record_update_timestamps || {}

  if name
    name = name.to_s
    send("#{name}=", value) # this works fine, sets article.user to user
    changes[name] = read_attribute(name) # this doesn't work; read_attribute returns nil for associations.
  end

  @changed_attributes.except!(*changes.keys)
  primary_key = self.class.primary_key
  self.class.update_all(changes, { primary_key => self[primary_key] }) == 1 # this doesn't work either; tries to update a column (user) which doesn't exist (should be updating user_id instead).
end

It either needs to be made clear that update_attribute does not work for associations (and preferably raise an exception if you try to do so, complaining that :user is not a database column in this example) or support it by detecting that you're passing an association and updating _id columns instead.