the first run of update.sh sets up a cron job to run itself
periodically. the update script takes one position argument, the git
branch to pull changes from, which is also known as "sysupdates channel"
- master for stable, dev for testing.
the sysupdates channel was lost in the cron job setup, always defaulting
to master (stable). this commit preserves the original arg value given
to update.sh during the initial run.
alex