Don't register if a non-bcache superblock is found as well
Use register_quiet for udev hook
make-bcache: Prevent stray superblocks

Fail if the device has any leftover superblock or partition table label.

Add a --wipe-bcache flag to overwrite bcache superblocks and recommend
wipefs for non-bcache superblocks.

Once the device is safe to write, always zero immediately before the
bcache superblock.

Make sure errors go to stderr.  Use pkg-config.