attachment redirects should be 301's rather than 302 #178

As reported in https://meta.trac.wordpress.org/ticket/4775 the attachment redirects should 301 (Permanent) to their respective locations rather than just 302'ing (Temporary)

Code ref: https://github.com/Automattic/o2/blob/master/o2.php#L968-L978

Start at o2.php lines 968-978, the code reference in the issue, and inspect how attachment redirects are generated. Verify that redirects to the respective attachment locations use a permanent 301 status rather than a temporary 302, while preserving their destinations.

Written by the indexing model from the issue text.