Added a migration generator

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@1477 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/lib/rails_generator/generators/components/migration/migration_generator.rb

+class MigrationGenerator < Rails::Generator::NamedBase
+  def manifest
+    record do |m|
+      m.directory File.join('db/migrate')
+      next_migration_number = Dir.glob("db/migrate/[0-9]*.*").size + 1
+      m.template 'migration.rb', File.join('db/migrate', "#{next_migration_number}_#{file_name}.rb")
+    end
+  end
+end

railties/lib/rails_generator/generators/components/migration/templates/migration.rb

+class <%= class_name %> < ActiveRecord::Migration
+  def self.up
+  end
+
+  def self.down
+  end
+end