Polymorphic find_or_create bug

Today I just spent 3 hours (and before a demo!) trying to figure out
why my polymorphic association fields were breaking.

Turns out someone else put in a patch for this 6 months ago. I'm not
sure if its the same solution I'd use... I'd rather find_or_create
attempt to use AssociationProxy#build if its available and only
Base#new if we're not on a proxy.

http://dev.rubyonrails.org/ticket/4645

Can someone on core look at this. I can do another version if anyone
would prefer. But, I'd love to have this fixed.

Thanks,
Hampton.

Well, the patch is outdated, but I have the tests merged. The
has_many patch was rejected so I still have to look at where that line
is being modified and add that to the edge version of the file.