[pve-devel] backup : add pigz compressor

[Dietmar Maurer]

> You could even make it so using pigz requires a setting in
> vzdump.conf. So in GUI you still can only select gzip or lzop.
> If set to gzip and vzdump.conf has pigz:on then pigz is used instead of gzip.
> Most novice users are only going to use the GUI, this would reduce the
> likelyhood of them turning on pigz and then complaiing about their
> decision.

Yes, that makes sense to me. Someone want to write a patch?