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

sha1_file.c

@@ -2251,7 +2251,7 @@ int move_temp_to_file(const char *tmpfile, const char *filename)
 			goto out;
 		ret = errno;
 	}
-	unlink(tmpfile);
+	unlink_or_warn(tmpfile);
 	if (ret) {
 		if (ret != EEXIST) {
 			return error("unable to write sha1 filename %s: %s\n", filename, strerror(ret));