module DelayedJob::NextMigrationVersion

def next_migration_number(dirname)

since ActiveRecord 3.0
while methods have moved around this has been the implementation 
def next_migration_number(dirname)
  next_migration_number = current_migration_number(dirname) + 1
  if ActiveRecord::Base.timestamped_migrations
    [Time.now.utc.strftime("%Y%m%d%H%M%S"), format("%.14d", next_migration_number)].max
  else
    format("%.3d", next_migration_number)
  end
end