mdconfig creating file based memory disk

[Quartz]

> It gives me double the size of 'swapfile' as swap space. It is obvious
> to me that this must fail.

Interestingly, I just tested this in a VM and it seems to work fine. I 
maxed out the ram by creating a few other ramdisks and filling them with 
dd zero files, and the most I got was a generic "out of swap space" 
error (no crashes or panics). Not sure exactly what it's doing though.