[SDL] Alpha again

[Lilith Calbridge]

Maybe I'm not understanding how to do this or even what alpha is about. 
I've got a display surface on which I've 

	SDL_SetAlpha (screen, SDL_SRCALPHA, 255);

The pixels I'm placing directly on the surface, after having blitted a
solid white background, have been OR'd with 0x20000000.  Should I not
see some indication of partial transparency.  I seem to be getting solid
colors in this test.

Thanks,
Lilith