Additional changes needed for Rails 4: migration_template calling sequence has changed; need new next_migration_number
http://api.rubyonrails.org/classes/Rails/Generators/Migration.html#method-i-migration_template
http://api.rubyonrails.org/v3.2.18/classes/Rails/Generators/Migration.html#method-i-migration_template
https://github.com/rails/rails/commit/3858a247bdab01c62d99a4d1307311ee346aa76e
Avoid Rails 4 mass assignment warning.