fahbackup: use bash -e and trap premature exits
fahrestore: use bash -e and trap premature exits
fahrestore: use smarter approach to trap premature exits
fahbackup: use smarter approach to trap premature exits
fahrestore: accommodate bash -e
fahbackup: accommodate bash -e
fahbackup: produce a warning if checkpoint file isn't found
fahbackup: indicate success with 'done' text
fahrestore: indicate success with 'done' text
fahbackup: don't ignore stderr of current->previous rename