Fix cron module for HP-UX

On HP-UX, the crontab command works like this, because there is no "-u" it's picky about the order of the arguments:

```
 crontab(1)                                                       crontab(1)
 NAME
      crontab - user job file scheduler
 SYNOPSIS
      crontab [file]
      crontab -e [username]
      crontab -l [username]
      crontab -r [username]
```

This patch ensures "crontab -l [username]" for reading, and "crontab [file]" for writing (same as SunOS).