Quaternion::angle shows halves actual angle

[kkolyan]

    use cgmath::InnerSpace;
    use cgmath::Quaternion;
    use cgmath::Rad;
    use cgmath::Rotation3;

    #[test]
    fn test2() {
        let identity = Quaternion::from_angle_y(Rad(0.0));

        let q = Quaternion::<f32>::from_angle_y(Rad(1.0));

        /*
           assertion `left == right` failed
             left: 1.0 rad
            right: 0.5 rad
        */
        assert_eq!(Rad(1.0), q.angle(identity));
    }

[kkolyan]

I see, this method is called on the inner Vector3 via deref, so it doesn't know that's about rotation