added a change url option

docs/changelog/6.x.x.txt

@@ -11,6 +11,8 @@
  - Run on registration and alert on new user have been converted to a single
    workflow.
  - Added a Photogallery prototype to the default installation.
+ - Added a change url function that will allow an editor to change the URL of
+   an asset permanently (circumventing normal versioning).
  - Added a wiki-like feature that will automatically bring a user to the
    create a page form if they are in admin mode, and click on a link to
    a page that doesn't exist yet.