Paper Trail compatibility

[dwbutler]

Hi,

I've been trying to get serialized_attributes and Paper Trail to work happily together. It turns out that Paper Trail depends on quite a few ActiveRecord features that didn't happen to be implemented for serialized attributes.

Instead of creating a bunch of different pull requests, I decided to lump everything together and just summarize what got changed.

• Fixed a bug where a reference to the 'data' field was hardcoded as data instead of using send(data_field).
• Added support for dirty attributes by calling attribute_will_change!.
• Overrode dup so it copies over a dup of the serialized data. Previously, the dup'ed object would keep a reference to the same serialized data as the original object. This fix is necessary because Paper Trail creates a version by duping the object, and then setting all attributes back to their previous values. So, modifying the dup was also modifying the serialized attributes on the original object.
• Added support for []= AKA write_attribute to modify serialized data.

[dwbutler]

I just realized I didn't add any specs for these changes. Let me know if these changes look good to you, and I'll go ahead and write some.

[technoweenie]

Are any of these ActiveRecord 3.x only? The changes look fine to me, but tests would be greatly appreciated :)

[dwbutler]

I'm pretty sure these will all work in ActiveRecord 2. I'll definitely cook up some tests!

[dwbutler]

Alright, I finished writing tests and verified that everything works in every ActiveRecord version and both Ruby 1.8.7 & 1.9.3. I would link to a Travis run, but I haven't been able to trigger a Travis run today, either automatically or manually.

[dwbutler]

Looks like Travis is working again. Everything is green!

[courtenay]

+1, this also handily removes a deprecation warning when running this plugin on 3.2-stable -rails/rails@50d395f

[technoweenie]

Sorry I'm terrible. We're not really using this gem anymore, so use at your own risk!