make a fabric command to update the location of cron.sh if this changes

[bepetersn]

The way I would like to handle this is the way we handle serving our static files currently. What we do there is to keep a symlink to a directory containing our static files. So, similarly, I think it would make sense to make a symlink to cron.sh, and have the crontab reference that symlink. This way, we can change our file if we want.