Reinstate the link checker

[alexwlchan]

This has been a TODO item in pre-flight-checks.sh since March.

Given that at least one broken link crept through in its absence (see #141), might be nice to turn it back on.

[inglesp]

So I've just had a go at fixing this (see inglesp/django-amber@bdbeeee)... but I hit this:

>>> requests.get('https://www.projectcalico.org/')
<Response [403]>

I can access the site fine with the browser...

Any ideas @alexwlchan?

[alexwlchan]

@inglesp I haven’t worked on Calico for a while, but I get the same problem.

I’d guess that something in the nginx config is causing it to drop the python-requests user agent, although I can’t think why. I’ll drop a line to the Calico folks and see if they have any ideas.

[alexwlchan]

Note that it doesn’t seem to be a certificate/HTTPS thing; I get the same result over HTTP:

>>> requests.get('https://www.projectcalico.org/')
<Response [403]>
>>> requests.get('http://www.projectcalico.org/')
<Response [403]>