Comment unused OSP_FB_ALPHA and warn about unsupported OSP_RGB_I8
Comment unused OSP_FB_ALPHA and warn about unsupported OSP_RGB_I8

Twinklebear/OSPRay,MengjiaoH/ospray,favreau/OSPRay,wilsonCernWq/ospray,ospray/OSPRay,MengjiaoH/ospray,ospray/OSPRay,favreau/OSPRay,MengjiaoH/ospray,ospray/OSPRay,ospray/OSPRay,MengjiaoH/ospray,favreau/OSPRay,wilsonCernWq/ospray,Twinklebear/OSPRay,MengjiaoH/ospray,Twinklebear/OSPRay,Twinklebear/OSPRay,favreau/OSPRay,wilsonCernWq/ospray