Put rel="noreferrer" on all nonlocal links
Ref T4342. By default, insert rel="noreferrer" for links. We do not insert this if:
- The caller provided an explicit "rel" attribute.
- We recognize the link as an anchor ("#comment-2"), or as local to the current domain ("/path/to/resource").
Otherwise, add it in all cases.
Reviewed By: btrahan
Maniphest Tasks: T4342
Differential Revision: https://secure.phabricator.com/D8711