- got rid of silly #define ..._BIT, #define ... (1<<..._BIT) stuff

- switched almost all uiDefBut(..., TOG|BIT|..) to use UiDefButBit and the
   name of the actual bit define instead of just a magic constant, this makes
   searching the code much nicer. most of the credit here goes to LetterRip
   who did almost all of the conversions, I mostly just checked them over.

source/blender/src/previewrender.c

@@ -652,12 +652,12 @@ static void texture_preview_pixel(Tex *tex, int x, int y, char *rect)
 			}
 			else {
 				skip= 1;
-				ta= 0.0;
+				tr= tg= tb= ta= 0.0;
 			}
 		}
 		else {
 			skip= 1;
-			ta= 0.0;
+			tr= tg= tb= ta= 0.0;
 		}
 	}
 	else {