[Rails-core] [PATCH] Add :dependent => :protect to has_many association (#3837)

[Diego Algorta Casamayou]

Hi.

I've submited a patch (http://dev.rubyonrails.org/ticket/3837) and
since it's my first attempt on extending rails I'd like you to review
it.

I'm wondering if my proceedings where "the right way" to do it or
should I do something else.

Thank you,
Diego