Ruby 2.0 compat

Fixes weird AR errors:

```
  NoMethodError: undefined method `insert_record' for #<Array:0x007fb0ca5fa7f8>
      gems/activerecord-2.3.14.github17/lib/active_record/associations/association_proxy.rb:149:in `send'
```

see http://tenderlovemaking.com/2012/09/07/protected-methods-and-ruby-2-0.html