Handle weird extensions on overrides. fixes #813.

Just a good guess based on the error message: Isn't rails all about intuition?

http://guides.rubyonrails.org/3_2_release_notes.html
> Passing formats or handlers to render :template and friends like render :template => "foo.html.erb" is deprecated. Instead, you can provide :handlers and :formats directly as options: render :template => "foo", :formats => [:html, :js], :handlers => :erb.