New user agent added for the Freebox.

The Freebox is the multimedia device of a french Internet provider: Free. This device provides a seedbox which uses the user agent "Mozilla/5.0". In the "Content-Disposition" header, if the "filename" key is used with the "filename*=UTF-8''" value, the seedbox does not take care about the header and saves the file name with the origin URL. This patch brings the support for the Freebox users.