backup: whitespace for btrfs send to be all on one line
backup: allow --lastsnapshot to print last snapshot for BACKUP
backup: add test() sub to use test shell cmd instead of perl tests
backup: add optional --ipmagic arg and pass it to all subs that need to run remotely
backup: add usage for --ipmagic=IPMAGIC
backup: add bash completion for --ipmagic=IPMAGIC
backup: implement remote running with --ipmagic