MINOR: http: Add 404 to http-request deny

This patch adds http status code 404 Not Found to http-request deny. See
issue #80.
diff --git a/include/common/http.h b/include/common/http.h
index 2d9bad7..d3519bc 100644
--- a/include/common/http.h
+++ b/include/common/http.h
@@ -83,6 +83,7 @@
 	HTTP_ERR_200 = 0,
 	HTTP_ERR_400,
 	HTTP_ERR_403,
+	HTTP_ERR_404,
 	HTTP_ERR_405,
 	HTTP_ERR_408,
 	HTTP_ERR_410,