Master/debian/wheezy

I recently realised that my bash completions are being shipped as part of the Debian packages for ZoL, which prompted me to make some updates.

These completions still aren't complete, but they now include full-featured completions for more of the commands (basically any which I use with any regularity in my day job). Existing completions are greatly improved over the original, significantly more useful if you have a lot of snapshots, and somewhat better in the case where you don't have access to /dev/zfs, but *do* have passwordless sudo set up for read-only commands, as suggested by ZoL.

I'm not sure if you actually use this repo as a working area at all, plus I recognise that having a number of commits for such a small feature might be an inappropriate level of detail, so feel free to ignore the pull request and just grab the file if you prefer.