#3960 Change links to use rel=nofollow instead of going through /nf/redirect?path=
All markdown-rendered links go through /nf/redirect which AFAIK was to avoid google juice going to external links. However, that is annoying and clean direct URLs are much more useful. We should generate regular direct URLs, and instead put rel=nofollow on the <a> tag.
rc/3960
To QA: put a link in a markdown area. Verify it hasn't been nf/redirect-converted.