Selecting an "alternative storage directory"

[VincentBeers@gmail.com]

This is kind of a personal feature request, but probably benefits other people too...

Basically, I have several external hard disks, and some of them usually try to mount /media/disk/. However, if I already have a disk in there, it mounts to /media/disk-1/ and Deluge will never find the correct location this way. It is a bit of a hassle to remount the disks in the correct order, and therefore my request is if alternative storage locations can be defined, so it can try to download to location #2 if location #1 was either not found or contains nothing (of course, if location 2 is empty too, it just downloads to location 1).

[mvoncken]

see #584