mmap: Don't use mmap by default on OS X.

It has little benefits in general, (esp. in our usecase) and huge disadvantages for files on network mounts.
"Basically, IOKit should be so fast and efficient, that there are few usecases left for mmap() on Darwin."

modules/access/mmap.c

@@ -58,8 +58,11 @@ vlc_module_begin();
     set_capability ("access", 52);
     add_shortcut ("file");
     set_callbacks (Open, Close);
-
+#ifdef __APPLE__
+    add_bool ("file-mmap", false, NULL,
+#else
     add_bool ("file-mmap", true, NULL,
+#endif
               FILE_MMAP_TEXT, FILE_MMAP_LONGTEXT, true);
 vlc_module_end();