Remove temporary warning
Merge commit '8ff0147' into reinstall-fix
Allow user modification of github_username

This allows devs working on the Dreamhack machine to update their
github_username value using edit-dreamhack-info.
Make check-github-account usage a bit more secure

Force input from STDIN rather than CLI arguments to reduce the chances of CLI
exploits occurring in code. (Later commits are going to introduce functionality
that will call check-github-account automatically as root with user-supplied
data. They'll be pre-filtered, of course, but I believe you can never be too
paranoid about this sort of thing.)
Revert "Remove temporary warning"

This reverts commit 1f32892feb6f5773ac385db67983a49a504829c1.

I had made this commit because I thought I would be committing this branch as a
whole to bring back the reinstaller. As it is, this is only the first part of
it.
Merge pull request #16 from Sophira/github-fixes

GitHub-related fixes