When applying changes or reseting changes create the right class

Before this patch after the changes are applied the changes can be only
accessed using string keys, but before symbols are also accepted.

After this change every state of the model will be consistent.

activemodel/lib/active_model/dirty.rb

@@ -167,13 +167,13 @@ def attribute_was(attr) # :nodoc:
       # Removes current changes and makes them accessible through +previous_changes+.
       def changes_applied
         @previously_changed = changes
-        @changed_attributes = {}
+        @changed_attributes = ActiveSupport::HashWithIndifferentAccess.new
       end
 
       # Removes all dirty data: current changes and previous changes
       def reset_changes
-        @previously_changed = {}
-        @changed_attributes = {}
+        @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
+        @changed_attributes = ActiveSupport::HashWithIndifferentAccess.new
       end
 
       # Handle <tt>*_change</tt> for +method_missing+.

activemodel/test/cases/dirty_test.rb

@@ -83,6 +83,14 @@ def save
     assert_not_nil @model.changes['name']
   end
 
+  test "be cosistent with symbols arguments after the changes are applied" do
+    @model.name = "David"
+    assert @model.attribute_changed?(:name)
+    @model.save
+    @model.name = 'Rafael'
+    assert @model.attribute_changed?(:name)
+  end
+
   test "attribute mutation" do
     @model.instance_variable_set("@name", "Yam")
     assert !@model.name_changed?