`each_with_object` is a Ruby 1.9 method, here re-implemented in core_ext.rb
in case it's missing (for older Ruby versions). Using `returning` is bad in
combination with Ruby on Rails because each usage of the method will emit
a Rails deprecation warning. This might be considered an Active Support bug,
but it's better to avoid using `returning` altogether and use `tap` from
Ruby 1.8.7, also re-implemented here in case it's missing.
Since existing usages or `returning` were better suited for `each_with_object`
than `tap`, they were rewritten using the former instead.
