#content_column and polymorphic columns

Hi !

I'm need to use ActiveRecord::Base#content_columns, but this method
does not filter out columns suffixed with _type, which is what
polymorphism uses.

I checked the 1.2 branch and trunk, and both don't do it:
http://dev.rubyonrails.org/browser/trunk/activerecord/lib/active_record/base.rb#L810

Is that considered a bug ? I'll whip up a test and patch if that is
indeed a bug.

Bye !