Change 'modify date' after extracting rar-archive

Previously when extracting an archive, the modified date is kept the same as the file inside the archive. This commit changes the modified date to be the same as the rar-file's date.

- This makes xbmc correctly determine the movie as recently added
- It is more consistent with how other files are downloaded, as the modified date will be changed to the current time when downloading a file (over torrent/http etc.)
- Since we copy the modified date from the rar-file, the date is set as expected when renaming older files (as opposed to using the current time)