Backport latest fallback list to 0.2.8 and 0.2.9

I'm generating a new list of fallback directory mirrors for release 0.2.9 in #18828 (moved).

We have a few options for dealing with the 0.2.8 list:

• comment-out any broken fallbacks,
• backport the 0.2.9 list,
• do nothing.

I would prefer to have the same src/or/fallback_dirs.inc in every (relevant) Tor release, assuming we do another 0.2.8 series release. This is consistent with how we handle directory authorities and geoip. Otherwise it becomes hard to check multiple fallback lists at once.

But I could be convinced to go with either of the other options.