DE28772 fix bug with removed attribute with setter

Addresses: [Defect DE28772: error when viewing MSB history](https://rally1.rallydev.com/#/11744709050d/detail/defect/15364528227)

The test case doesn't fail when using Rails 3, only issues a warning:

```
DEPRECATION WARNING: You're trying to create an attribute `sacrificial_column'. Writing arbitrary attributes on a model is deprecated. Please just use `attr_writer` etc. (called from block (2 levels) in reify at /Users/dorleans/paper_trail/lib/paper_trail/version.rb:72)
```

I tried upgrading to use Rails 4 but ran into trouble and it didn't seem worthwhile.  But I'm pretty sure this would cause an exception rather than a deprecation warning.