Correctly handle GitHub error messages. Hopefully.
Temporarily add always-changing etag for testing
Try logging the github error on fetching user data
Try outputting GitHub Error status code
Try to handle 401-3 errors better.

If we get a 401, 402 or 403 error from the GitHub API, we'll now
redirect to /auth-revoked/ which will print out a special publication
page suggesting the user re-authenticates.

Hopefully this works OK. Not sure if this is likely to interfere with
likely errors during the original authentication process...
Fix display of standard errors