Added AR:B#dup method for duplicationg object without frozen attributes [#2859 state:resolved]

Signed-off-by: Yehuda Katz + Carl Lerche <ykatz+clerche@engineyard.com>

activerecord/lib/active_record/base.rb

@@ -2870,6 +2870,13 @@ def frozen?
         @attributes.frozen?
       end
 
+      # Returns duplicated record with unfreezed attributes.
+      def dup
+        obj = super
+        obj.instance_variable_set('@attributes', instance_variable_get('@attributes').dup)
+        obj
+      end
+
       # Returns +true+ if the record is read only. Records loaded through joins with piggy-back
       # attributes will be marked as read only since they cannot be saved.
       def readonly?

activerecord/test/cases/base_test.rb

@@ -2116,4 +2116,8 @@ def test_create_with_custom_timestamps
       assert_equal custom_datetime, parrot[attribute]
     end
   end
+
+  def test_dup
+    assert !Minimalistic.new.freeze.dup.frozen?
+  end
 end