ACT_SURFACE_ALPHA_REJECTION_VALUE, Auto param that bind pass alpha rejection value.

New auto param, named ACT_SURFACE_ALPHA_REJECTION_VALUE (surface_alpha_rejection_value in programs scripts), that bind the alpha rejection value stored in the material pass.
It does not give alpha rejection value as in Ogre:ass::getAlphaRejectionValue(), but convert it instead to a [0.0; 1.0] floating point value (255.0f / Ogre:ass::getAlphaRejectionValue()).
Very usefull to handle alpha rejection in shadows, compositor shaders, or deferred rendering.