specify target directory for restore

From http://www.mysqlperformanceblog.com/2009/02/24/xtrabackup-open-source-alternative-for-innodb-hot-backup-call-for-ideas/#comment-488852

"I was always upset with the fact the restore (ibbackup –apply-log) restores the ibdata and log files *in the same path* as the backup files. This made for harder work when disk space is limited.
The backup stage allows for different paths, which is nice. If you could have this simple feature - it would make a great difference."