Setting $args now invalidates unparsed uri

* Merge nginx hg commit (changeset 5699:e9dbffc18a77)
* See http://forum.nginx.org/read.php?29,246766,246766 for details
* This commit also fixes this [lua test case 014-bugs.t:TEST 38](https://github.com/openresty/lua-nginx-module/blob/master/t/014-bugs.t#L866).