xfsprogs: Add verifiers to libxfs buffer interfaces.

xfsprogs: Add verifiers to libxfs buffer interfaces.

Verifiers need to be used everywhere to enable calculation of CRCs
during writeback of modified metadata. Add then to the libxfs buffer
interfaces conver the internal use of devices to be buftarg aware.

Verifiers also require that the buffer has a back pointer to the
struct xfs_mount. To make this source level comaptible between
kernel and userspace, convert userspace to pass struct xfs_buftargs
around rather than a "device".

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>