Issues/1190

$a->query_string keep the query string from server.
We rewrite "server/page/arg?a=b" as "server/index.php?pagename=page/arg&a=b", so query string from server is "pagename=page/arg&a=b" and $a->query_string value is "page/arg&a=b".
$a->query_string is used as value for $_SESSION['return_url'], here the issue raised in #1190 

This commit modify the value of $a->query_string to "page/arg?a=b"