[arch-releng] btrfs fs can now be used "directly" in AIF

[Dieter Plaetinck]

We've discussed in detail why we should discourage users from doing this
(although I actually only heard Anthony raise his concerns) - see 
http://mailman.archlinux.org/pipermail/arch-releng/2010-December/001341.html

It's turning out impractical to expect any kind of support for such advanced btrfs schemes (where we somehow enforce or even just support subvolumes) in AIF.
So for now I just allow users to use the btrfs directly.
See commit https://github.com/Dieterbe/aif/commit/281b49fd3dd0984805a9dc435d1a2c36c675eb4d

This will at least enable people to actually use and test btrfs.

Dieter