[tz] [PROPOSED] Prefer https: URLs and bring some URLs up to date

[Paul Eggert]

On 09/25/2017 02:59 PM, Gilmore Davidson wrote:
> The basic process was planned to be along these lines:
> 1. Find all reference URLs in data source comments.
> 2. For each link, do a HEAD request to get the HTTP headers of the URL:
>      * If the URL still works, move on.
>      * If the status code is a 301 permanent redirect, update the reference to the new URL.
>      * If the domain no longer resolves, or the URL returns a 404 not found, make a request to the Web Archive API to find the latest cached version of that page, and update the reference URL accordingly.

This sounds reasonable, except that for our three HTML files I have 
preferred to remove dead links rather than to point to the Wayback Machine.

Also, how portable was the prototype script?