removed the ERROR_COLOUR macro
removed a useless case where ERROR_COLOUR is returned when no object intersection is found from pixel_colour_from_ray()
changed nearest_object_intersecting_ray() to deal with different return values from ray_object_intersect()
moved hitlocation and hitnormal calculations into specific ray_object_intersect() functions
changed the default return value of ray_object_intersect() to none
removed object_normal_at_point() and related tests
changed from infinity to none as return value of the intersection functions when no intersetion is found
git-svn-id: http://svn.plouj.com/repos/eraytracer@59 b8c14938-b733-429d-887c-d66ed1f8cd15