cp: improvements

- improve copying block, char devices, fifo and sockets with -a.
- improve exit status code.

cp.c

@@ -49,5 +49,5 @@ main(int argc, char *argv[])
 	if(argc > 2 && !(stat(argv[argc-1], &st) == 0 && S_ISDIR(st.st_mode)))
 		eprintf("%s: not a directory\n", argv[argc-1]);
 	enmasse(argc, argv, cp);
-	return EXIT_SUCCESS;
+	return cp_status;
 }