eager loading and polymorphic associations

There is a dedicated section about eager loading in the docs. A coworker discovered eager loading does not work in polymorphic associations the hard way :slight_smile: so I've written a patch that documents it:

    http://dev.rubyonrails.org/ticket/10610

There are at least a couple of tickets that implement something that would change that though:

    http://dev.rubyonrails.org/ticket/9640
    http://dev.rubyonrails.org/ticket/8119

What do you think?

-- fxn

Committed. Thanks Xavier!

#9640 will be dipping its toes into trunk soon too.

jeremy