Fix bugs in DnS java downloader

we have an application for downloading it has bugs: 1. download speed is not always determined sometimes we can to download the file to 15 MB and not see the correct value, because it shows 0 kb / s 2. sometimes you can not choose the directory for download in finder: <[login to view URL]> 3. sometimes "Remaining items" does not show the correct value: <[login to view URL]> 4. sometimes "checking" takes too long time, looks like bug. 5. sometimes some files in downloading list does not download: <[login to view URL]>