Fixes and misc improvements

I made some fixes for rsnapshot:
- eae0bd58 issue with SSH command parameters
- ff14a5eb7 issue with pod2man not in /usr/bin
- 71c9cd2b copy/paste issue in rsnapshot-diff

I also made a couple of improvements:
- 33e7ef35 backup_script destination optional
- fabc7b0b detecting busybox version of logger (which does not like the -i option)

Pick any of those if you find they are interesting, I'll maintain them anyways for my own version of rsnapshot :)