Merge branch 'ar/unlink-err' into maint

* ar/unlink-err:
  print unlink(2) errno in copy_or_link_directory
  replace direct calls to unlink(2) with unlink_or_warn
  Introduce an unlink(2) wrapper which gives warning if unlink failed

diff.c

@@ -189,7 +189,7 @@ static void remove_tempfile(void)
 	int i;
 	for (i = 0; i < ARRAY_SIZE(diff_temp); i++) {
 		if (diff_temp[i].name == diff_temp[i].tmp_path)
-			unlink(diff_temp[i].name);
+			unlink_or_warn(diff_temp[i].name);
 		diff_temp[i].name = NULL;
 	}
 }