add a migrate class method and delegate to the new instance

activerecord/lib/active_record/migration.rb

@@ -329,10 +329,13 @@ class << self
     end
 
     def self.method_missing(name, *args, &block) # :nodoc:
-      self.delegate = self.new
       (delegate || superclass.delegate).send(name, *args, &block)
     end
 
+    def self.migrate(direction)
+      new.migrate direction
+    end
+
     cattr_accessor :verbose
 
     attr_accessor :name, :version