patch 8.0.1236: Mac features are confusing

Problem:    Mac features are confusing.
Solution:   Make feature names more consistent, add "osxdarwin". Rename
            feature flags, cleanup Mac code. (Kazunobu Kuriyama, closes #2178)
diff --git a/src/os_macosx.m b/src/os_macosx.m
index d6913d4..029f103 100644
--- a/src/os_macosx.m
+++ b/src/os_macosx.m
@@ -8,20 +8,16 @@
  */
 
 /*
- * os_macosx.m -- Mac specific things for Mac OS/X.
+ * os_macosx.m -- Mac specific things for Mac OS X.
  */
 
-#ifndef MACOS_X_UNIX
-    Error: MACOS 9 is no longer supported in Vim 7
-#endif
-
 /* Avoid a conflict for the definition of Boolean between Mac header files and
  * X11 header files. */
 #define NO_X11_INCLUDES
 #define BalloonEval int   /* used in header files */
 
 #include "vim.h"
-#import <Cocoa/Cocoa.h>
+#import <AppKit/AppKit.h>
 
 
 /*