* Don't remove it on update. If you have it now, you'll keep it. New installs won't get it.
* Peform a redirect using rewrite + canonical to the new location, if the file doesn't exist.
props SergeyBiryukov.
fixes#18544.
git-svn-id: https://develop.svn.wordpress.org/trunk@20596 602fd350-edb4-49c9-b593-d223f7449a82