EZP-23437: rewrite rules update for nginx

> Required by [EZP-23437](http://jira.ez.no/browse/EZP-23437) / ezsystems/ezpublish-kernel#1031


Stored images (`var/[dir/]images[-versioned]/*`) are now sent to Sf's `index.php` instead of legacy's `index_cluster.php`
I second @andrerom here. 
Imho, if someone wants to get 5.3 from github he should check 5.3 branch and in that branch docs like this should avoid things like 'if you are  in...'
I think that conditions add a bit of noise...