libxfs: modify verifiers to differentiate CRC from other errors

libxfs: modify verifiers to differentiate CRC from other errors

[userspace port]

Modify all read & write verifiers to differentiate
between CRC errors and other inconsistencies.

This sets the appropriate error number on bp->b_error,
and then calls xfs_verifier_error() if something went
wrong.  That function will issue the appropriate message
to the user.

Also, fix the silly bug in xfs_buf_ioerror() that this patch
exposes.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>