When behind a captive portal whose landing page has a certificate error, you can get in a weird situation where the landing page itself shows the captive portal interstitial.

We should fix this to only show the captive portal interstitial if there is a COMMON_NAME_INVALID error. Otherwise, we're showing an inaccurate error (we're saying that the problem is that you have to connect to the wifi, when you're already trying to connect to the wifi but can't), plus it's not overridable so there's no way to connect.

(Example: https://twitter.com/paulschreiber/status/829510620085157889)