Fix changelog indent, remove self from method call in changelog/doc examples

[ci skip]

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
-*   Fix ActiveRecord `subclass_from_attrs` when eager_load is false.
+*   Fix ActiveRecord `subclass_from_attrs` when `eager_load` is false.
     It cannot find subclass because all classes are loaded automatically
     when it needs.
 
@@ -24,7 +24,7 @@
     Example:
 
         sql = Post.connection.unprepared_statement do
-            Post.first.comments.to_sql
+          Post.first.comments.to_sql
         end
 
     *Cédric Fabianski*
@@ -106,7 +106,8 @@
     Example:
 
         class ChangeEnum < ActiveRecord::Migration
-          self.disable_ddl_transaction!
+          disable_ddl_transaction!
+
           def up
             execute "ALTER TYPE model_size ADD VALUE 'new_value'"
           end

activerecord/lib/active_record/migration.rb

@@ -339,7 +339,8 @@ def initialize
   # you can turn the automatic transactions off.
   #
   #   class ChangeEnum < ActiveRecord::Migration
-  #     self.disable_ddl_transaction!
+  #     disable_ddl_transaction!
+  #
   #     def up
   #       execute "ALTER TYPE model_size ADD VALUE 'new_value'"
   #     end