Resolve Octokit::TooManyRequests once and for all

[Mailaender]

Octokit::TooManyRequests: GET https://api.github.com/repos/OpenRA/OpenRA/releases/2280129: 403 - API rate limit exceeded for 52.0.240.122. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.) // See: https://developer.github.com/v3/#rate-limiting

See #253 for my failed attempts. Maybe caching the file sizes/links and doing the lookup only when necessary (final push prior to release) might already lessen the problem.

[pchote]

I am assuming that the rate limit is done per build slave / ip, not per project, based on the fact that restarting the build a few times will eventually succeed. Reducing our lookups won't help if that is the case, because the limit depends on all projects that run on that server.

[phrohdoh]

Indeed it is per-IP.