before_filter that responds_to mime types

Hi all,

Sorry for the double post. I forgot to change the subject. :frowning:

I have a small enhancement to actioncontroller that I'd like reviewed.
It's a before_filter that respond_to different mime types.
http://dev.rubyonrails.org/ticket/11118

I have added tests and documentation too. Please review it, and if
it's to your liking +1 it. Otherwise, let me know what else I'd need
to do to get it committable. Thanks.

Wilhelm