rem: KNSavedArticle* KNFolder::byId(int id) { int idx=findId(id); if(idx!=-1) return ((KNSavedArticle*)list[idx]); else return 0; }
add: KNLocalArticle* byId(int id)        { return static_cast<KNLocalArticle*>(KNArticleCollection::byId(id)); }
context: KNSavedArticle* KNFolder::byId(int id){  int idx=findId(id);  if(idx!=-1) return ((KNSavedArticle*)list[idx]);  else return 0;}