`edit.php?post_type=attachment` should redirect to `upload.php`. Without the redirect, the user is presented with an empty list table. There are probably other issues to address overall, but this accomplishes what the ticket wants.

Props knutsp.
Fixes #27951.

Built from https://develop.svn.wordpress.org/trunk@28729


git-svn-id: http://core.svn.wordpress.org/trunk@28543 1a063a9b-81f0-0310-95a4-ce76da25c4cd