Adding encryption to Btrfs

I'd hesitate to consider the lack of progress on the encryption front to be evidence of stagnation; I certainly spent some time harping at cmason and company that encryption was not something that should be attempted without encryption experts getting involved. My harps were mostly of the "obvious approach A will cause non-obvious failure modes 1, 2, 3", and I don't feel they needed much convincing at the time (or maybe cmason and josef will say anything to shut me up :p).