Rails Pending Migration Errors
Raise errors in development mode when there are pending migrations to run.
It is essentially a backport of this feature that made it in Rails 4.

Note: this has only been tested against Rails 3.2.13 on ruby 2.0.0p247.
Installation
Add this line to your application's Gemfile:
gem 'rails_pending_migration_errors', group: :development
And then execute:
$ bundle