Add some attribute readers to migration module.

railties/lib/generators/active_record/migration/templates/migration.rb

@@ -1,4 +1,4 @@
-class <%= @migration_class_name %> < ActiveRecord::Migration
+class <%= migration_class_name %> < ActiveRecord::Migration
   def self.up<% attributes.each  do |attribute| %>
     <%= migration_action %>_column :<%= table_name %>, :<%= attribute.name %><% if  migration_action == 'add' %>, :<%= attribute.type %><% end  -%>
   <%- end %>

railties/lib/generators/active_record/model/templates/migration.rb

@@ -1,4 +1,4 @@
-class <%= @migration_class_name %> < ActiveRecord::Migration
+class <%= migration_class_name %> < ActiveRecord::Migration
   def self.up
     create_table :<%= table_name %> do |t|
 <% for  attribute in attributes -%>

railties/lib/generators/active_record/session_migration/templates/migration.rb

@@ -1,4 +1,4 @@
-class <%= @migration_class_name %> < ActiveRecord::Migration
+class <%= migration_class_name %> < ActiveRecord::Migration
   def self.up
     create_table :<%= session_table_name %> do |t|
       t.string :session_id, :null => false

railties/lib/generators/migration.rb

@@ -5,6 +5,11 @@ module Rails
     # just by implementing the next migration number method.
     #
     module Migration
+      def self.included(base) #:nodoc:
+        base.send :attr_reader, :migration_number,
+                                :migration_file_name,
+                                :migration_class_name
+      end
 
       # Creates a migration template at the given destination. The difference
       # to the default template method is that the migration number is appended