MINOR: http-htx: Store messages of an http-errors section in a http reply array

Error messages specified in an http-errors section is now also stored in an
array of http replies. So, for now, these messages are stored as a buffer and as
a http reply.
diff --git a/include/types/http_htx.h b/include/types/http_htx.h
index b24b47f..e6752c1 100644
--- a/include/types/http_htx.h
+++ b/include/types/http_htx.h
@@ -85,6 +85,7 @@
 	} conf;                               /* config information */
 
 	struct buffer *errmsg[HTTP_ERR_SIZE]; /* customized error messages for known errors */
+	struct http_reply *replies[HTTP_ERR_SIZE]; /* HTTP replies for known errors */
 	struct list list;                     /* http-errors list */
 };