new disk format pushed to btrfs-unstable

Hello everyone,

I've pulled in David's NFS changes and directory hashing change. This means the btrfs-unstable tree now has a new disk format.

All of the critical performance and stability fixes are in the btrfs-stable tree, without disk format changes. I'll continue putting anything important there until the next release.

Thanks to David and Balaji Rao for getting NFS support working!

-chris