Changes

* Possibly the best compromise is to treat the source URL as canonical only if the destination has never been visited from somewhere else. If the destination is visited from somewhere else, we undo it and treat the destination as canonical. Bookmarks on the destination should always be assigned to the destination page regardless of canonicalization. This gets around the security problems (at worst, the user sees a funny URL in history, and then only for pages they've never seen before), while preserving most of the functionality for legitimate temporary redirects.

== Approach ==