Temporary changes in multiblock.DiffOp. Change traction operators in Elastic2dvariable to be true boundary operators. But adjoint FD conv test fails for dirichlet BC so need to debug!

function A = spdiag(a,i)
    default_arg('i',0);

    if isrow(a)
        a = a';
    end

    n = length(a)+abs(i);
    A = spdiags(a,i,n,n);
end