shagr4th

Here's my patch, rebased on trunk. It's quite large, but this feature was a hard one ;) Please be aware that I had no prior knowledge of this project codebase, so I tried my best to respect the general "philosophy". I added some basic unit tests but I need to add more. Thanks for the review

Hi all, FWIW, I managed to make a patch for this. This was a non trivial feature to add (more so than a bug). The best strategy to my eyes was to manage node duplication at the compilation level : each field references is duplicated as well, while taking care of the subscript index (on multiple levels if necessary). Also, doing it this way allows us to add support of a CONTROL clause (in the screen section, same as the MF one), so we can change screen attribute / color of the nth occurence at runtime....