Ok, here you go -- this was applied to the source tree of Apache 1.3.3
(same warning about munged whitespace, use patch -l i think..)

        -- Larry

-----
*** util.c.orig Thu May 13 21:28:46 1999
--- util.c      Thu May 13 21:30:45 1999
***************
*** 1108,1115 ****
   *   bad % escape       returns BAD_REQUEST
   *
   *   decoding %00 -> \0
-  *   decoding %2f -> /   (a special character)
   *                      returns NOT_FOUND
   */
  API_EXPORT(int) ap_unescape_url(char *url)
  {
--- 1108,1116 ----
   *   bad % escape       returns BAD_REQUEST
   *
   *   decoding %00 -> \0
   *                      returns NOT_FOUND
+  *   decoding %2f -> /   (a special character)
+  *                      returns success
   */
  API_EXPORT(int) ap_unescape_url(char *url)
  {
***************
*** 1128,1134 ****
            else {
                url[x] = x2c(&url[y + 1]);
                y += 2;
!               if (url[x] == '/' || url[x] == '\0')
                    badpath = 1;
            }
        }
--- 1129,1135 ----
            else {
                url[x] = x2c(&url[y + 1]);
                y += 2;
!               if (url[x] == '\0')
                    badpath = 1;
            }
        }