simple validation to be able to run migrations with :table_name_with_underscore #15051

This validation fix the issue with https://github.com/rails/rails/issues/15051 schema_migrations.
I followed @raeno instructions to reproduce it.
Run his repo https://github.com/raeno/rails-4-schema-migration-id
And I created another app with very similar config to run against my local:
https://github.com/joseluistorres/my-test-app