Btrfs: Better block record keeping, real mkfs

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --cc fs/btrfs/Makefile
Simple merge

diff --cc fs/btrfs/ctree.h
Simple merge

diff --cc fs/btrfs/debug-tree.c
Simple merge

diff --cc fs/btrfs/dir-test.c
Simple merge

diff --cc fs/btrfs/disk-io.c
Simple merge

diff --cc fs/btrfs/extent-tree.c
Simple merge

diff --cc fs/btrfs/mkfs.c
Simple merge