Btrfs-progs: Initialize stripesize to sectorsize.

The minimum extent size should be equal to the blocksize.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
make_btrfs: Fix superblock writing to the disk.

The patch enables mkfs.btrfs() to work when
sectorsize != BTRFS_SUPER_INFO_SIZE.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Btrfs-progs: Allow subpagesize-blocksize btrfs instances to be created.

Signed-off-by: chandan <chandan@linux.vnet.ibm.com>