Merge pull request rails#6619 from kennyj/fix_6591

Fix rails#6591 Rails 3.2.5 Regression: incorrect _changed? for datetimes

activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb

@@ -57,8 +57,9 @@ def #{attr_name}=(original_time)
                   time = time.is_a?(String) ? Time.zone.parse(time) : time.to_time rescue time
                 end
                 time = time.in_time_zone rescue nil if time
+                changed = read_attribute(:#{attr_name}) != time
                 write_attribute(:#{attr_name}, original_time)
-                #{attr_name}_will_change!
+                #{attr_name}_will_change! if changed
                 @attributes_cache["#{attr_name}"] = time
               end
             EOV

activerecord/test/cases/dirty_test.rb

@@ -78,6 +78,17 @@ def test_time_attributes_changes_with_time_zone
       assert_equal old_created_on, pirate.created_on_was
     end
   end
+
+  def test_setting_time_attributes_with_time_zone_field_to_itself_should_not_be_marked_as_a_change
+    in_time_zone 'Paris' do
+      target = Class.new(ActiveRecord::Base)
+      target.table_name = 'pirates'
+
+      pirate = target.create
+      pirate.created_on = pirate.created_on
+      assert !pirate.created_on_changed?
+    end
+  end
 
   def test_time_attributes_changes_without_time_zone_by_skip
     in_time_zone 'Paris' do