messages: mark some strings with "up-to-date" not to touch

The treewide clean-up of "up-to-date" strings done in 7560f547
(treewide: correct several "up-to-date" to "up to date", 2017-08-23)
deliberately left some out, but unlike the lines that were changed
by the commit, the lines that were deliberately left untouched by
the commit is impossible to ask "git blame" to link back to the
commit that did not touch them.

Let's do the second best thing, leave a short comment near them
explaining why those strings should not be modified or localized.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
[es: make in-code comment more developer-friendly]
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/send-pack.c

@@ -338,6 +338,7 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 	}
 
 	if (!ret && !transport_refs_pushed(remote_refs))
+		/* stable plumbing output; do not modify or localize */
 		fprintf(stderr, "Everything up-to-date\n");
 
 	return ret;