Comment 4 for bug 1181789

The setting of proc->script was introduced here:

http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/saucy/upstart/saucy/revision/1182.62.1

At the moment it doesn't seem to be tested anywhere other than in job_process_run(), so simply reverting the change should fix the problem, but presumably this was intended to be useful later, as the comment says "That way tests can reliably check for shell-specific behaviour."