Dirty checking on serialize attributes hides changes on concurrent updates

The solution of #788 partial_updates clobbers serialized attributes to save all serialize attributes creates a problem with concurrent changes on two or more serialized columns. Bug #2397 serialized attributes clobbered on partial updates doesn't solve it either, because it still finds the two defined serialize attributes.

I currently reverted the behaviour to before #788 partial_updates clobbers serialized attributes by commenting out the extra added dirty attributes. Could this become a setting to automaticly add these serialize attributes if needed? Or create a nice way of turning this default behaviour off?

      def update_with_dirty
        if partial_updates?
          # Serialized attributes should always be written in case they've been
          # changed in place.
          update_without_dirty(changed) # | self.class.serialized_attributes.keys)
        else
          update_without_dirty
        end
      end

User Story: I currently have two jquery sorted lists. When an item is dragged to the other list both the lists put an array of ordered integers into the same record. When this is handled concurrent the dirty checking adds both serialize fields by default and updates both fields twice. The last one wins and items are removed or duplicated.