Any installations attempted from the new golang.org/dl/ site will fail (i.e. Go 1.2.2. Go 1.3 and newer).

This is because the JSON contains a URL like "http://golang.org/dl/..." but this is actually an HTTP 302 redirect to somewhere else.

Jenkins cannot handle HTTP 30x redirects when downloading tools automatically, so this fails — see JENKINS-23507.

Until that is fixed, the temporary workaround should be to have the backend-crawler follow the redirects, so that Jenkins doesn't have to follow them.
But this is fragile and not a good idea in general (i.e. we don't want to be breaking mirror networks etc.).