blackbox: add backup bundle paths to blackbox logs Writes the backup bundle paths to the blackbox so it's easy to see which backup bundle is associated with which command when you are debugging an issue. Example output: 2013/03/13 10:39:56 durham> strip tip 2013/03/13 10:39:59 durham> saved backup bundle to /data/users/durham/www-hg/.hg/strip-backup/e5fac262363a-backup.hg 2013/03/13 10:40:03 durham> strip tip exited 0 after 7.97 seconds