comparing old dir children and new dir children - executed on change event
@param {String} parentId directory id
@param {Object} old_children old directory children
@param {Object} descendants directory descendants
@returns {Array}  recognized changes
function compareDirFiles(parentId, old_children, descendants){
    var changes = [],
        not_found = object.extend({}, old_children);
    
    for(var id in descendants) {
        if(descendants[id].ancestors[ descendants[id].ancestors.length-1 ] === parentId) { // compare only direct children
            
            if(!old_children[id]) { // not found in current children - created
                changes.push({ event:'created', file:descendants[id] });
                old_children[id] = descendants[id];
            }
            else if(old_children[id].modifiedDT < descendants[id].modifiedDT) { // found and updated
                changes.push({ event:'updated', file:descendants[id] });
                old_children[id] = descendants[id];
                delete not_found[id];
            }
            else { // file found, not not updated
                delete not_found[id];
            }
        }
    }
    
    // removed files
    for(var id in not_found) {
        changes.push({ event:'removed', file:not_found[id] });
        delete old_children[id];
    }
    
    return changes;
}