Added an "updated" variable to detect whether the install/symlink functions
updated their target. Cleaned up the way I remove "success" files.
Switched back to password prompting sudo use, drastically simplifies code and
check-config is interactive anyway.
Changed install and symlink functions to have more informative (and working!)
sudo password prompts.
Added proper automatic tarsnap backups for OSX.

--HG--
rename : dotfiles/tarsnaprc => install/tarsnap/tarsnap.conf
Added notifications for backup failures.