rails/rails — pull request #4491 by pkondzior (2012-01-17 07:26:39+00:00)
Title: Wrong behavior of ActiveModel::Errors#dup is causing regressions on Rails master

Since ActiveModel::Errors instance keeps all error messages as hash
we should duplicate this object as well.

Previously ActiveModel::Errors was a subclass of ActiveSupport::OrderedHash,
which results in different behavior on `dup`, this may result in regression for
people relying on it.

I'm attaching also small cleanup of redundant code.