mailinfo: strip "RE: " prefix

We already strip the more common Re: and re:, and we do not often
see RE: from saner MUA, but this prefix does exist and gets used
from time to time.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/mailinfo.c

@@ -232,7 +232,9 @@ static void cleanup_subject(struct strbuf *subject)
 		case 'r': case 'R':
 			if (subject->len <= at + 3)
 				break;
-			if (!memcmp(subject->buf + at + 1, "e:", 2)) {
+			if ((subject->buf[at + 1] == 'e' ||
+			     subject->buf[at + 1] == 'E') &&
+			    subject->buf[at + 2] == ':') {
 				strbuf_remove(subject, at, 3);
 				continue;
 			}