(svn r9884) -Feature: 2 new zoom-out levels: 8 times and 16 times

-Codechange: unified the blitter function so we have 1 function for all zoom-levels
-Codechange: make most of the label functions work with zoom-level instead of magic numbers and big switches per zoom-level
-Codechange: MakeXXXDirty() functions didn't take into account zoom-level, but just used the biggest possible value
-Codechange: simplified blitter functions to avoid code duplication

src/zoom.hpp

@@ -10,6 +10,8 @@ enum ZoomLevel {
 	ZOOM_LVL_NORMAL = 0,
 	ZOOM_LVL_OUT_2X,
 	ZOOM_LVL_OUT_4X,
+	ZOOM_LVL_OUT_8X,
+	ZOOM_LVL_OUT_16X,
 	ZOOM_LVL_END,
 
 	/* Here we define in which zoom viewports are */
@@ -26,19 +28,21 @@ enum ZoomLevel {
 	ZOOM_LVL_DETAIL   = ZOOM_LVL_OUT_2X, //! All zoomlevels below or equal to this, will result in details on the screen, like road-work, ...
 
 	ZOOM_LVL_MIN      = ZOOM_LVL_NORMAL,
-	ZOOM_LVL_MAX      = ZOOM_LVL_OUT_4X,
+	ZOOM_LVL_MAX      = ZOOM_LVL_OUT_16X,
 };
 
 extern ZoomLevel _saved_scrollpos_zoom;
 
 static inline int ScaleByZoom(int value, ZoomLevel zoom)
 {
+	if (zoom == ZOOM_LVL_NORMAL) return value;
 	int izoom = (int)zoom - (int)ZOOM_LVL_NORMAL;
 	return (zoom > ZOOM_LVL_NORMAL) ? value << izoom : value >> izoom;
 }
 
 static inline int UnScaleByZoom(int value, ZoomLevel zoom)
 {
+	if (zoom == ZOOM_LVL_NORMAL) return value;
 	int izoom = (int)zoom - (int)ZOOM_LVL_NORMAL;
 	return (zoom > ZOOM_LVL_NORMAL) ? value >> izoom : value << izoom;
 }