Copy changed_attributes across to newly become'd records

Without this, the original record's values won't get saved, since the partial insertions support (144e8691cb) checks for changed values and thinks there are none.

activerecord/lib/active_record/persistence.rb

@@ -181,6 +181,7 @@ module ActiveRecord
       became = klass.new
       became.instance_variable_set("@attributes", @attributes)
       became.instance_variable_set("@attributes_cache", @attributes_cache)
+      became.instance_variable_set("@changed_attributes", @changed_attributes)
       became.instance_variable_set("@new_record", new_record?)
       became.instance_variable_set("@destroyed", destroyed?)
       became.instance_variable_set("@errors", errors)

activerecord/test/cases/persistence_test.rb

@@ -152,6 +152,20 @@ class PersistenceTest < ActiveRecord::TestCase
     assert_equal original_errors, client.errors
   end
 
+  def test_dupd_becomes_persists_changes_from_the_original
+    original = topics(:first)
+    copy = original.dup.becomes(Reply)
+    copy.save!
+    assert_equal "The First Topic", Topic.find(copy.id).title
+  end
+
+  def test_becomes_includes_changed_attributes
+    company = Company.new(name: "37signals")
+    client = company.becomes(Client)
+    assert_equal "37signals", client.name
+    assert_equal %w{name}, client.changed
+  end
+
   def test_delete_many
     original_count = Topic.count
     Topic.delete(deleting = [1, 2])