Pull Request: Notify A User they Have Pending Migrations On Specific Exceptions

I wrote a pull request to inform developers that they have pending
migrations and should run `rake db:migrate` whenever they get a
NoMethodError or UnknownAttributeError on an AR object and their
database isn't migrated to the last version.

I've gotten several community members to comment, but I would like
some feedback from the Rails team:

https://github.com/rails/rails/pull/4165

Thanks for your time.