die_errno(): double % in strerror() output just in case

[tr: handle border case where % is placed at end of buffer]

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

usage.c

@@ -64,8 +64,24 @@ void die_errno(const char *fmt, ...)
 {
 	va_list params;
 	char fmt_with_err[1024];
+	char str_error[256], *err;
+	int i, j;
 
-	snprintf(fmt_with_err, sizeof(fmt_with_err), "%s: %s", fmt, strerror(errno));
+	err = strerror(errno);
+	for (i = j = 0; err[i] && j < sizeof(str_error) - 1; ) {
+		if ((str_error[j++] = err[i++]) != '%')
+			continue;
+		if (j < sizeof(str_error) - 1) {
+			str_error[j++] = '%';
+		} else {
+			/* No room to double the '%', so we overwrite it with
+			 * '\0' below */
+			j--;
+			break;
+		}
+	}
+	str_error[j] = 0;
+	snprintf(fmt_with_err, sizeof(fmt_with_err), "%s: %s", fmt, str_error);
 
 	va_start(params, fmt);
 	die_routine(fmt_with_err, params);