Fixed some failing specs and added the aria2 downloader

I fixed some of the broken specs where the urls had changed a little or a video had been deleted. I also skipped the arte.tv spec as it is currently failing again. Maybe you could take a look at it rb2k if you have time? So right now it's Dailymotion, Vimeo and arte.tv that have broken plugins.

I also added aria2 (http://aria2.sourceforge.net/) to the list of download tools. The main thing with aria2 is that it can do multiple connection for a single file downloads over HTTP, so you can get some pretty nice speed gains if the server is throttling the speed for a single connection.