Add support for direct to remote data directory for test and new slave systems

Request option to backup (via rsync) to a remote test system or new slave, directly into the data directory. The problem with this is that the script wants to create a unique folder under the destination (which in this case, is not wanted, since I'd like to be able to reset a test server or slave without having to allocate extra space or resend files that haven't changed since the last time).

I tried removing the prefix and date format arguments but the prefix is currently mandatory. I also thought of using backuptype=none and the beforebackup hook but that seemed less than ideal since it wouldn't relate to a backup success/failure and wouldn't trigger any associated events or logging. Perhaps a new boolean arg such as disableautoverdir (disable auto version directory) or a relaxing of the mandatory prefix constraint.