Problem in vmath::lookat

[Froser]

There is a problem in vmath.h:1060.
template
static inline Tmat4 lookat(const vecN<T,3>& eye, const vecN<T,3>& center, const vecN<T,3>& up)
{
const Tvec3 f = normalize(center - eye);
const Tvec3 upN = normalize(up);
const Tvec3 s = cross(f, upN);
const Tvec3 u = cross(s, f);
const Tmat4 M = Tmat4(Tvec4(s[0], u[0], -f[0], T(0)),
Tvec4(s[1], u[1], -f[1], T(0)),
Tvec4(s[2], u[2], -f[2], T(0)),
Tvec4(T(0), T(0), T(0), T(1)));

return M * translate<T>(-eye);

}

I think we must guarantee that vector s and vector u are normalized, otherwise we cannot ensure matrix M is correct.(And in fact in some cases, M is incorrect).
So I changed them into:
const Tvec3 s = normalize(cross(f, upN));
const Tvec3 u = normalize(cross(s, f));