Fix caching on first save for an unused model

[kratob]

On certain code paths, saving an instance of a model for the first time can cause the cache column not to be written. Affected code looks like this:

class Model < ActiveRecord::Base
  acts_as_taggable_on
end

record = Model.new
record.tag_list = 'foo, 'bar'
record.save!
record.tag_list   # => nil

The reason for this is that the after_save hook gets dynamically added when calling Model.columns. However, Model.new does not actually do that.

The fix uses Model.load_schema! instead.

[judithroth]

This would be really useful to us. Is there something that blocks merging this (apart from the conflicts that are now there because the MR is quite old)?
We would happily update the MR (or provide a new one) if there is a chance that this gets merged.

[FLeinzi]

Is there any chance to bring this PR up-to-date?