scheduled backup over a network

[dnanian]

As indicated in the User's Guide, we can't copy directly to a network volume (you cannot authorize across a network and get full rights to the far-side share, at least not without running an "agent" on the other side that does the I/O for you).

So, we'll write to a disk image on the far side. And, we'll automatically mount the network drive, mount the image, copy to the image and unmount the image when the schedule time comes.