Mime::Type.register in 1.1.6

Hi,

According to the documentation in
actionpack/lib/action_controller/mime_responds.rb

we should register custom mime types using
Mime::Type.register "image/jpg", :jpg

However, this method does not exist in mime_type.rb.
It exists in trunk, but not in the 1.1.6 tag.

Am I looking in the wrong place?

Thanks.
Jon