Show real file size on systems with ZFS compression enabled.

[zyansheep]

Hi, just noticed that on two different machines, the same files have very different sizes despite them being the same file (I moved a copy from one machine to another just to be sure).

I think this is due to dua not taking into account ZFS compression when calculating file sizes. Just thought I'd submit this issue in case anyone comes across it in the future and wants to take a crack at fixing it :)