AppKit: convert parameter-only macros to file-scope functions

- CABackingStore PIXEL, CPDragServer DRAGGING_WINDOW,
  CPOutlineView SELECTION_SHOULD_CHANGE and SHOULD_SELECT_ITEM
  become plain functions; call syntax is unchanged at all sites
- these macros reference only their parameters, so no ambient state
  is involved

AppKit/CoreAnimation/CABackingStore.j

@@ -23,7 +23,10 @@
 @import "CGGeometry.j"
 @import "CPCompatibility.j"
 
-#define PIXEL(pixels) pixels + "px";
+function PIXEL(pixels)
+{
+    return pixels + "px";
+}
 
 
 function CABackingStoreGetContext(aBackingStore)