Ensure that CollectionAssociation#replace returns proper target

The fix commited in e2a070c was returning the `new_target`, as
a try to return whatever user replaced association with. The
problem is, the resulting association target may be ordered
differently. In such case we want to return the target that
will be later used for that association.

Author: drogus

activerecord/lib/active_record/associations/collection_association.rb

@@ -492,7 +492,7 @@ def replace_records(new_target, original_target)
                                   "new records could not be saved."
           end
 
-          new_target
+          target
         end
 
         def concat_records(records)

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -1687,14 +1687,14 @@ def test_replace
     assert_equal [bulb2], car.reload.bulbs
   end
 
-  def test_replace_returns_new_target
+  def test_replace_returns_target
     car = Car.create(:name => 'honda')
     bulb1 = car.bulbs.create
     bulb2 = car.bulbs.create
     bulb3 = Bulb.create
 
     assert_equal [bulb1, bulb2], car.bulbs
-    result = car.bulbs.replace([bulb1, bulb3])
+    result = car.bulbs.replace([bulb3, bulb1])
     assert_equal [bulb1, bulb3], car.bulbs
     assert_equal [bulb1, bulb3], result
   end