bug #1340

Key alpha (render) set alph component at '1' for sky... this is an old
convention from NeoGeo days, and I have absolutely no clue whatfor...
maybe for some antique amiga iff format or so. Made it zero now.

source/blender/render/intern/source/rendercore.c

@@ -247,7 +247,7 @@ void scanlinesky(char *rect, int y)
 	if(R.r.alphamode & R_ALPHAKEY) {
 		
 		cp= (char *)&col;
-		cp[3]= 1;
+		cp[3]= 0;
 		cp[0]= 255.0*R.wrld.horr;
 		cp[1]= 255.0*R.wrld.horg;
 		cp[2]= 255.0*R.wrld.horb;